Seth Thomas Pocket Watch Mainsprings

This page documents Seth Thomas pocket watch mainspring specifications from the 1904 Seth Thomas Watch Material Catalog and compares them with later replacement mainsprings sold by outside suppliers. The examples shown here help identify replacement spring numbers, package labels, factory numbers, model sizes, and Dennison gauge references used for Seth Thomas pocket watches.

The 1904 Seth Thomas Watch Material Catalog No. 650 - October 1, 1904

The 1904 Seth Thomas Watch Material Catalog No. 650 - October 1, 1904, describes the:

Model 1 - Factory Part No. 23 - Mainspring with patent brace, as 21.5 inches long, .132 wide, .0075 thick, or, 24 wide, 3 thick Dennison gauge.

Model 2, Model 3, and Model 4 - Factory Part No. 140 - Mainspring 1st quality, with patent brace, as 21.5 inches long, .132 wide, .0075 thick, or, 24 wide, 3 thick Dennison gauge.

Model 2, Model 3, and Model 4 - Factory Part No. 141 - Mainspring 2nd quality, as 20 inches long, .132 wide, .009 thick, or, 24 wide, 1¼ thick Dennison gauge.

Model 5 - Factory Part No. 339 - Mainspring with patent brace, as 21.5 inches long, .132 wide, .0075 thick, or, 24 wide, 3 thick Dennison gauge. Note 1 tells us that “Movements Nos. 300,000 to 350,000 are 7 jewels and are made with same mainspring, yoke, yoke screw, and setting arm as in model No. 6”

Model 5 High Grade Railroad Movements - Factory Part No. 436 - Mainspring, extra quality, 21.5 inches long, .132 wide, .0075 thick, or, 24 wide, 3 thick Dennison gauge.

Model 6 and Model 7 Eagle Series Old Model - Factory Part No. 536 - Mainspring with patent brace, as 20 inches long, .132 wide, .009 thick, or, 24 wide, 1¼ thick, Dennison gauge.

Model 8 and Model 9 Eagle Series New Model - Factory Part No. 633 - Mainspring with patent brace, as 20 inches long, .116 wide, .009 thick, or, 20 wide, 1¼ thick, Dennison gauge.

Model 10 and Model 11 Century Old Model - Factory Part No. 729 - Mainspring with patent brace, as 20 inches long, .132 wide, .009 thick, or, 24 wide, 1¼ thick, Dennison gauge.

Model 12 and Model 13 Century New Model - Factory Part No. 828 - Mainspring with patent brace, as 20 inches long, .116 wide, .009 thick, or, 20 wide, 1¼ thick, Dennison gauge.

Model 14 - Factory Part No. 927 - Mainspring with patent brace, as 17 inches long, .076 wide, .0065 thick, or, 10 wide, 4½ thick Dennison gauge.

Model 15 - Factory Part No. 1026 - Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.

Model 16 - Factory Part No. 1026 - Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.

Model 17 - Factory Part No. 1026 - Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.

Model 18 - Factory Part No. 1119 - Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.

Original Seth Thomas Pocket Watch Mainspring Packaging

The factory mainspring packaging shown above demonstrates standardized size-based distribution with designated fields for required information. The original “Seth Thomas Watch Main Springs” label has been crossed out, indicating that the box was repurposed to hold mainsprings of a different mainspring manufacturer and/or specifications than it originally contained.

Alternative Manufacturers of Mainsprings for Seth Thomas Pocket Watches

In addition to original Seth Thomas mainsprings, replacement mainsprings for Seth Thomas pocket watches were also offered by other manufacturers and material suppliers. The examples below document alternative manufacturers, package numbers, stated Seth Thomas applications, and any measurements printed on the original packaging. The metric units used on the packaging are confusing when trying to compare and cross-reference the mainsprings. For the purpose of clarity, the metric units used on the Mainspring Cross-Reference Chart below for the mainspring lengths have all been expressed in centimeters and the metric units used for mainspring width and thickness have all been expressed in millimeters regardless of how they were expressed on the packaging.

H R Alloy and Sandsteel replacement mainspring packaging identify Seth Thomas 16-size and 12-size applications using the same respective numbers, 2106 and 2521. These entries are listed as inferred Seth Thomas factory part numbers because they are not currently documented in surviving Seth Thomas material catalogs reviewed for this project.

Seth Thomas Pocket Watch Mainspring Cross-Reference
Manufacturer Mfr. Part No. ST Application Factory Part No. Length Width Thickness Dennison Details
Original Seth Thomas / 1904 Watch Material Catalog No. 650
Seth Thomas 23 Model 1 23 21.5 inches .132 .0075 24 wide, 3 thick Mainspring with patent brace.
Seth Thomas 140 Model 2, Model 3, and Model 4 140 21.5 inches .132 .0075 24 wide, 3 thick 1st QUALITY; with patent brace.
Seth Thomas 141 Model 2, Model 3, and Model 4 141 20 inches .132 .009 24 wide, 1¼ thick 2nd QUALITY.
Seth Thomas 339 Model 5 339 21.5 inches .132 .0075 24 wide, 3 thick With patent brace. Catalog note states movements Nos. 300,000 to 350,000 are 7 jewels and use the same mainspring, yoke, yoke screw, and setting arm as Model 6.
Seth Thomas 436 Model 5 High Grade Railroad Movements 436 21.5 inches .132 .0075 24 wide, 3 thick EXTRA QUALITY.
Seth Thomas 536 Model 6 and Model 7 Eagle Series Old Model 536 20 inches .132 .009 24 wide, 1¼ thick With patent brace.
Seth Thomas 633 Model 8 and Model 9 Eagle Series New Model 633 20 inches .116 .009 20 wide, 1¼ thick With patent brace.
Seth Thomas 729 Model 10 and Model 11 Century Old Model 729 20 inches .132 .009 24 wide, 1¼ thick With patent brace.
Seth Thomas 828 Model 12 and Model 13 Century New Model 828 20 inches .116 .009 20 wide, 1¼ thick With patent brace.
Seth Thomas 927 Model 14 927 17 inches .076 .0065 10 wide, 4½ thick With patent brace.
Seth Thomas 1026 Model 15 1026 17 inches .076 .0075 10 wide, 3 thick With patent brace.
Seth Thomas 1026 Model 16 1026 17 inches .076 .0075 10 wide, 3 thick With patent brace.
Seth Thomas 1026 Model 17 1026 17 inches .076 .0075 10 wide, 3 thick With patent brace.
Seth Thomas 1119 Model 18 1119 17 inches .076 .0075 10 wide, 3 thick With patent brace.
Inferred Seth Thomas Factory Part Nos. from Alternate Manufacturers' Retail Packaging or Catalogs
Seth Thomas 536 ST 18-size 536 not stated 3.30 mm 0.195 thick 24 wide, 3 3/4 thick From 1944 Sandsteel Catalog No. 12
Seth Thomas 729 ST 18-size 729 not stated 3.30 mm 0.225 thick 24 wide, 1 1/2 thick From 1944 Sandsteel Catalog No. 12
Seth Thomas 828 ST 18-size 828 not stated 2.90 mm 0.225 thick 20 wide, 1 1/2 thick From 1944 Sandsteel Catalog No. 12
Seth Thomas 927 ST 6-size 927 not stated 1.90 mm 0.16 thick 10 wide, 6 1/2 thick From 1944 Sandsteel Catalog No. 12
Seth Thomas 1026 ST 6-size 1026 not stated 1.90 mm 0.195 thick 10 wide, 3 3/4 thick From 1944 Sandsteel Catalog No. 12
Seth Thomas 1441 ST 0-size 1441 not stated 1.50 mm 0.15 thick 6 wide, 7 thick From 1944 Sandsteel Catalog No. 12
Seth Thomas 2106 Model 21 2106 21 inches 2.35 mm 0.23 mm 14 1/2 wide, 1 thick 16-Size
Seth Thomas 2521 Model 22 or 23 2521 21 inches 1.95 mm 0.205 mm 10 1/2 wide, 3 thick 12-Size
Original Seth Thomas Package Example
Seth Thomas not stated ST 12-size not stated not stated not stated not stated not stated .234 as marked on original package.
Alternative Manufacturers and Material Suppliers
Black Shield 4397 ST 18-size No. 536 No. 536 20 1/4 inches / 51.10 cm 3.30 mm 0.195 thick 24 wide, 3 1/4 thick Swartchild & Co., Chicago.
Black Shield 4399 A ST 12-size New Model not stated not stated not stated not stated not stated Swartchild & Co., Chicago.
Black Shield 4400 ST 6-size Century No. 1026 not stated not stated not stated not stated Swartchild & Co., Chicago.
Charles Robert 701 ST 18-size No. 536 not stated 3.30 mm 0.185 thick 24 wide, 4½ thick Swiss Made
Charles Robert 705 ST 12-size not stated not stated not stated 0.205 not stated Swiss Made
Charles Robert 706 ST 6-size No. 1026 not stated 1.9mm 0.205 thick 10 wide, 3 thick Swiss Made
Diamond 76 Model 1 23 not stated not stated not stated not stated Benj. Allen & Co.
Diamond 149 Model 3 140 / 141 not stated not stated not stated not stated Same as Diamond Part No. 76, Benj. Allen & Co.
Diamond 220 Model 2 140 / 141 not stated not stated not stated not stated Same as Diamond Part No. 76, Benj. Allen & Co.
Diamond 271 Model 4 140 / 141 not stated not stated not stated not stated Same as Diamond Part No. 76, Benj. Allen & Co.
E. & J. Swigart Co. A 1175 ST 18-size No. 828 not stated 2.90 mm 0.225 thick 20 wide, 1½ thick All Jewels
E. & J. Swigart Co. 702 ST 18-size 18-size All Models 20 1/2 inches 3.30 mm 0.22 thick 24 wide, 2 thick Illustrated Manual of American Watch Movements, SETH THOMAS and CENTURY
E. & J. Swigart Co. 703 ST 18-size 18-size All Models 20 1/2 inches 2.90 mm 0.22 thick 24 wide, 2 thick Illustrated Manual of American Watch Movements, SETH THOMAS and CENTURY
E. & J. Swigart Co. 704 ST 16-size 16-size All Models 18 1/2 inches 2.40 mm 0.23 thick 15 wide, 1 thick Illustrated Manual of American Watch Movements, SETH THOMAS and CENTURY
E. & J. Swigart Co. 705 ST 12-size 12-size All Models 16 1/2 inches 2.00 mm 0.21 thick 11 wide, 3 thick Illustrated Manual of American Watch Movements, SETH THOMAS and CENTURY
E. & J. Swigart Co. 707 ST 6-size 6-size All Models 14 1/2 inches 1.90 mm 0.15 thick 10 wide, 7 thick Illustrated Manual of American Watch Movements, SETH THOMAS and CENTURY
Etiquette Inc. 520 ST 18-size No. 536 54.50 cm / 21½ inches 3.30 mm 0.19 thick 24 wide, 4½ thick Made in Switzerland.
The Fulton Wine Color ST 18-size not stated not stated not stated 0.19 thick not stated No Retaining Clamp
HR Alloy SA 652 ST 18-size No. 536 T Brace 21½ inches 3.30 mm 0.19 thick 24 wide, 2 thick No Retaining Clamp
HR Alloy SA 653 ST 18-size No. 729 T Brace 30 inches 3.30 mm 0.22 thick 24 wide, 2 thick Made in Switzerland.
HR Alloy A 654 ST 16-size No. 2106 21 inches 2.35 mm 0.23 thick 14 1/2 wide, 1 thick Made in Switzerland.
HR Alloy SA 655 ST 12-size No. 2521 21 inches 1.95 mm 0.205 thick 10 1/2 wide, 3 thick Made in Switzerland.
KBK 3033 ST 16-size T end not stated not stated 2.34 mm 0.22 thick 15 wide, 2 thick Kilb, Beck, Kuesel, Inc.
Marco 1001 ST 18-size New Style No. 536 20 1/4 inches not stated not stated 24 wide, 3 3/4 thick not stated
Marco 1002 ST 18-size Century, wider Factory No. 729 No. 729 not stated not stated not stated not stated not stated
Marco 1010 ST 16-size No. ___ not stated not stated not stated not stated Made in Switzerland.
Marco 1030 ST 12-size T end not stated not stated not stated not stated not stated Made in Switzerland.
Nu Vigor 1072 ST 18-size No. 141 53.34 cm / 21 inches 3.30 mm 0.22 thick 24 wide, 2 thick Made in Switzerland.
Nu Vigor 1073 ST 18-size No. 536 53.98 cm / 21 1/4 inches 3.30 mm 0.195 thick 24 wide, 3 3/4 thick, 21 1/4 long Made in Switzerland.
Nu Vigor 1074 ST 18-size No. 729 50.80 cm / 20 inches 3.30 mm 0.22 thick 24 wide, 1 1/2 thick Made in Switzerland.
Nu Vigor 1075 ST 18-size No. 828 50.80 cm / 20 inches 2.90 mm 0.22 thick 20 wide, 2 thick Made in Switzerland.
Sandsteel 536 ST 18-size No. 536 not stated 3.30 mm 0.195 thick 24 wide, 3 3/4 thick From 1944 Sandsteel Catalog No. 12
Sandsteel 729 ST 18-size No. 729 not stated 3.30 mm 0.225 thick 24 wide, 1 1/2 thick From 1944 Sandsteel Catalog No. 12
Sandsteel 828 ST 18-size No. 828 not stated 2.90 mm 0.225 thick 20 wide, 1 1/2 thick From 1944 Sandsteel Catalog No. 12
Sandsteel 927 ST 6-size No. 927 not stated 1.90 mm 0.16 thick 10 wide, 6 1/2 thick From 1944 Sandsteel Catalog No. 12
Sandsteel 1026 ST 6-size No. 1026 not stated 1.90 mm 0.195 thick 10 wide, 3 3/4 thick From 1944 Sandsteel Catalog No. 12
Sandsteel 1441 ST 0-size No. 1441 not stated 1.50 mm 0.15 thick 6 wide, 7 thick From 1944 Sandsteel Catalog No. 12
Sandsteel 2106 ST 16-size No. 2106 not stated 2.40 mm 0.22 thick 15 wide, 2 thick Made in U.S.A. by Watch-Motor Mainspring Co. Inc. New York
Sandsteel 2521 ST 12-size No. 2521 not stated 2.00 mm 0.20 thick 11 wide, 3 1/2 thick Made in U.S.A. by Watch-Motor Mainspring Co. Inc. New York
Unit Resilient 1002 ST 18-size Century not stated not stated not stated 0.22 thick not stated not stated
Unit Resilient not stated ST 6-size not stated not stated not stated 0.15 thick not stated Made by Waltham Watch Company Waltham, USA
U.S.R. not stated ST 18-size Old Style No. 23 not stated not stated not stated not stated not stated
U.S.R. not stated ST 18-size No. 536 No. 536 not stated not stated not stated not stated not stated
U.S.R. not stated ST 12-size not stated not stated not stated not stated not stated not stated

View a printable PDF version of the Seth Thomas Mainspring Cross-Reference Chart

Jump to a Specific Manufacturer’s Record Illustrated Below

Black Shield‍ ‍Charles Robert‍ ‍E. & J. Swigart Co.‍ ‍Etiquette‍ ‍The Fulton‍ ‍H R Alloy

KBK‍ ‍Marco‍ ‍Nu Vigor‍ ‍Sandsteel‍ ‍Unit Resilient‍ ‍U.S.R.‍ ‍

Additional Sources Consulted / Future Evidence Sought

Black Shield Mainspring No. 4397 Package of 12

Black Shield Mainspring No. 4397 box of 12, for Seth Thomas 18-size movements cross-referenced to Seth Thomas Factory Part No. 536. Factory Part No. 536 was used primarily in Seth Thomas Model 6 and Model 7 movements, and also in 7-jewel Seth Thomas Model 5 movements marked with serial numbers 300,000 to 350,000.

Black Shield Mainspring Package No. 4397 – Seth Thomas 18-size No. 536
Black Shield Mainspring Alternate Package No. 4397 – Seth Thomas 18-size No. 536 (spring in waxed paper is not retained by a clamp)
Black Shield Mainspring No. 4397 – Seth Thomas 18-size No. 536
Black Shield Mainspring Package No. 4399 A – Seth Thomas 12-size New Model
Black Shield Mainspring No. 4399 A – Seth Thomas 12-size New Model

Black Shield

Black Shield Mainspring Package No. 4397 – Seth Thomas 18-size No. 536

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‍

Seth Thomas Model 6 and Model 7

Model 5 ser#’s 300,000 to 350,000

Black Shield Mainspring No. 4397 – Seth Thomas 18-size No. 536

Black Shield Mainspring Package No. 4399 A – Seth Thomas 12-size New Model

Seth Thomas 12-size

Black Shield Mainspring Alternate Package No. 4397 – Seth Thomas 18-size No. 536 (spring in waxed paper is not retained by a clamp)

Black Shield Mainspring No. 4399 A – Seth Thomas 12-size New Model

Black Shield Mainspring Package No. 4400 – Seth Thomas 6-size Century No. 1026

Seth Thomas 6-size Century Model 18

Black Shield Mainspring No. 4400 – Seth Thomas 6-size Century No. 1026

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Black Shield Mainspring Package No. 4400 – Seth Thomas 6-size Century No. 1026
Charles Robert Mainspring Package No. 701 – for Seth Thomas 18-size Factory No. 536, 3.30 centimeters wide, 0.185 thick, or, 24 wide, 4½ thick Dennison gauge
Charles Robert Mainspring No. 701 – for Seth Thomas 18-size Factory No. 536, 3.30 millimeters wide, 0.185 thick, or, 24 wide, 4½ thick Dennison gauge
Charles Robert Mainspring Package No. 705 – for Seth Thomas 12-size .0205
Charles Robert Mainspring No. 705 – for Seth Thomas 12-size .205

Charles Robert

Charles Robert Mainspring Package No. 701 – for Seth Thomas 18-size Factory No. 536, 3.30 millimeters wide, 0.185 thick, or, 24 wide, 4½ thick Dennison gauge

Seth Thomas Model 6 and Model 7

Model 5 ser#’s 300,000 to 350,000

Charles Robert Mainspring No. 701 – for Seth Thomas 18-size Factory No. 536, 3.30 millimeters wide, 0.185 thick, or, 24 wide, 4½ thick Dennison gauge

Charles Robert Mainspring Package No. 706 – for Seth Thomas 6-size Factory No. 1026, 1.9 millimeters wide, 0.205 thick, or, 10 wide, 3 thick Dennison gauge.

Seth Thomas 6-size

Charles Robert Mainspring No. 706 – for Seth Thomas 6-size Factory No. 1026, 1.9 millimeters wide, 0.205 thick, or, 10 wide, 3 thick Dennison gauge.

Charles Robert Mainspring Package No. 705 – for Seth Thomas 12-size .205

Seth Thomas 12-size

Charles Robert Mainspring No. 705 – for Seth Thomas 12-size .205

Charles Robert Mainspring Package No. 706 – for Seth Thomas 6-size Factory No. 1026, 1.9 millimeters wide, 0.205 thick, or, 10 wide, 3 thick Dennison gauge.
Charles Robert Mainspring No. 706 – for Seth Thomas 6-size Factory No. 1026, 1.9 millimeters wide, 0.205 thick, or, 10 wide, 3 thick Dennison gauge.

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E. & J. Swigart Co. Mainspring Package No. A 1175 – for Seth Thomas 18-size Factory No. 828, 20 wide, 1½ thick Dennison gauge; .22½
E. & J. Swigart Co. Mainspring No. A 1175 – for Seth Thomas 18-size Factory No. 828, 20 wide, 1½ thick Dennison gauge; .22½

E. & J. Swigart Co.

E. & J. Swigart Co. Mainspring Package No. A 1175 – for Seth Thomas 18-size Factory No. 828, 20 wide, 1½ thick Dennison gauge; .22½

‍ Seth Thomas Century Models 12 & 13

E. & J. Swigart Co. Mainspring No. A 1175 – for Seth Thomas 18-size Factory No. 828, 20 wide, 1½ thick Dennison gauge; .22½

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Etiquette Inc. Mainspring Packaging No. 520 – for Seth Thomas 18-size Factory No. 536, 3.30 centimeters wide, 54.40 long, 0.19 thick, or, 24 wide, 4½ thick Dennison gauge, 21½ inches long
Etiquette Inc. Mainspring Packaging No. 520 – for Seth Thomas 18-size Factory No. 536, 3.30 millimeters wide, 54.40 long, 0.19 thick, or, 24 wide, 4½ thick Dennison gauge, 21½ inches long

Etiquette Inc.

Etiquette Inc. Mainspring Packaging No. 520 – for Seth Thomas 18-size Factory No. 536, 3.30 millimeters wide, 54.40 long, 0.19 thick, or, 24 wide, 4½ thick Dennison gauge, 21½ inches long

Seth Thomas Model 6 & 7

Model 5 ser#’s 300,000 to 350,000

Etiquette Inc. Mainspring No. 520 – for Seth Thomas 18-size Factory No. 536, 3.30 millimeters wide, 54.40 long, 0.19 thick, or, 24 wide, 4½ thick Dennison gauge, 21½ inches long

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The Fulton

The Fulton “Wine Color” Mainspring Package– for Seth Thomas 18-size, .019 thick

Seth Thomas 18-size

The Fulton “Wine Color” Mainspring – for Seth Thomas 18-size, .019 thick

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HR Alloy Mainspring Package No. SA 652 – for Seth Thomas 18-size Factory No. 536 T Brace, 21½ inches long, 3.30 millimeters wide, 0.19 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland
HR Alloy Mainspring No. SA 652 – for Seth Thomas 18-size Factory No. 536 T Brace, 21½ inches long, 3.30 millimeters wide, 0.19 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland

HR Alloy

HR Alloy Mainspring Package No. SA 652 – for Seth Thomas 18-size Factory No. 536 T Brace, 21½ inches long, 3.30 millimeters wide, 0.19 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland

Seth Thomas Model 6 & 7

Model 5 ser#’s 300,000 to 350,000

HR Alloy Mainspring No. SA 652 – for Seth Thomas 18-size Factory No. 536 T Brace, 21½ inches long, 3.30 millimeters wide, 0.19 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland

HR Alloy Mainspring Package No. SA 653 – for Seth Thomas 18-size Factory No. 729 T Brace, 30 inches long, 3.30 millimeters wide, 0.22 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland

‍ Seth Thomas Century Models 10 & 11

HR Alloy Mainspring No. SA 653 – for Seth Thomas 18-size Factory No. 729 T Brace, 30 inches long, 3.30 millimeters wide, 0.22 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland

HR Alloy Mainspring Package No. A 654 – for Seth Thomas 16-size Factory No. 2106, 21 inches long, 2.35 millimeters wide, 0.23 thick, or, 14½ wide, 1 thick Dennison gauge - Made in Switzerland

Seth Thomas 16-size Centennial Model 21

HR Alloy Mainspring No. A 654 – for Seth Thomas 16-size Factory No. 2106, 21 inches long, 2.35 millimeters wide, 0.23 thick, or, 14½ wide, 1 thick Dennison gauge - Made in Switzerland

HR Alloy Mainspring Package No. A 655 – for Seth Thomas 12-size Factory No. 2521, 21 inches long, 1.95 millimeters wide, 0.205 thick, or, 10½ wide, 3 thick Dennison gauge - Made in Switzerland

Seth Thomas 12-size

HR Alloy Mainspring No. A 655 – for Seth Thomas 12-size Factory No. 2521, 21 inches long, 1.95 millimeters wide, 0.205 thick, or, 10½ wide, 3 thick Dennison gauge - Made in Switzerland

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HR Alloy Mainspring No. SA 653 – for Seth Thomas 18-size Factory No. 729 T Brace, 30 inches long, 3.30 millimeters wide, 0.22 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland
HR Alloy Mainspring Package No. A 654 – for Seth Thomas 16-size Factory No. 2106, 21 inches long, 2.35 millimeters wide, 0.23 thick, or, 14½ wide, 1 thick Dennison gauge - Made in Switzerland
HR Alloy Mainspring Package No. A 655 – for Seth Thomas 12-size Factory No. 2521, 21 inches long, 1.95 millimeters wide, 0.205 thick, or, 10½ wide, 3 thick Dennison gauge - Made in Switzerland
HR Alloy Mainspring No. A 655 – for Seth Thomas 12-size Factory No. 2521, 21 inches long, 1.95 millimeters wide, 0.205 thick, or, 10½ wide, 3 thick Dennison gauge - Made in Switzerland
HR Alloy Mainspring Package No. SA 653 – for Seth Thomas 18-size Factory No. 729 T Brace, 30 inches long, 3.30 millimeters wide, 0.22 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland

KBK

Kilb, Beck, Kuesel, Inc Mainspring Package No. 3033 – for Seth Thomas 16-size, 2.34 millimeters wide, 0.22 thick, or, 15 wide, 2 thick Dennison gauge

Seth Thomas 16-size Centennial Model 21

Kilb, Beck, Kuesel, Inc Mainspring No. 3033 – for Seth Thomas 16-size, 2.34 millimeters wide, 0.22 thick, or, 15 wide, 2 thick Dennison gauge

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Marco Mainspring Package No. 1001 – for Seth Thomas 18-size New Style Factory No. 536
Marco Mainspring Alt Package No. 1001 - Width 24, Strength 3¾, Length 20¼ – for Seth Thomas 18-size New Style Factory No. 536
Marco Mainspring No. 1001 – for Seth Thomas 18-size New Style Factory No. 536
Marco Mainspring No. 1002 – for Seth Thomas 18-size Century, wider, Factory No. 729 - Made in Switzerland
Marco Mainspring Package No. 1010 – for Seth Thomas 16-size New Style Factory No. ___ - Made in Switzerland
Marco Mainspring No. 1010 – for Seth Thomas 16-size New Style Factory No. ___ - Made in Switzerland
Marco Mainspring Package No. 1030 – for Seth Thomas 12-size T end - Made in Switzerland
Marco Mainspring No. 1030 – for Seth Thomas 12-size T end - Made in Switzerland

Marco

Marco Mainspring Package No. 1001 – for Seth Thomas 18-size New Style Factory No. 536

Seth Thomas Model 6 & 7

Model 5 ser#’s 300,000 to 350,000

Marco Mainspring Alternative Package No. 1001 - Width 24, Strength 3¾, Length 20¼ – for Seth Thomas 18-size New Style Factory No. 536

Marco Mainspring No. 1001 – for Seth Thomas 18-size New Style Factory No. 536

Marco Mainspring Package No. 1010 – for Seth Thomas 16-size New Style Factory No. ___ - Made in Switzerland

Seth Thomas 16-size Centennial Model 21

Marco Mainspring No. 1010 – for Seth Thomas 16-size New Style Factory No. ___ - Made in Switzerland

Marco Mainspring Package No. 1030 – for Seth Thomas 12-size T end - Made in Switzerland

Seth Thomas 12-size

Marco Mainspring No. 1030 – for Seth Thomas 12-size T end - Made in Switzerland

Marco Mainspring Package No. 1002 – for Seth Thomas 18-size Century, wider, Factory No. 729 - Made in Switzerland

‍ ‍Seth Thomas Century Models 10 & 11

Marco Mainspring No. 1002 – for Seth Thomas 18-size Century, wider, Factory No. 729 - Made in Switzerland

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Nu Vigor Mainspring No. 1072 – for Seth Thomas 18-size Factory No. 141
Nu Vigor Mainspring Package No. 1073 – for Seth Thomas 18-size Factory No. 536 – 53.98 centimeters long, 3.30 wide, .195 thick, or, 24 wide, 3¾ thick, 21¼ inches long Dennison gauge - Made in Switzerland
Nu Vigor Mainspring No. 1073 – for Seth Thomas 18-size Factory No. 536 – 53.98 centimeters long, 3.30 wide, .195 thick, or, 24 wide, 3¾ thick, 21¼ inches long Dennison gauge - Made in Switzerland
Nu Vigor Mainspring Package No. 1074 – for Seth Thomas 18-size Factory No. 729 – 50.80 centimeters long, 3.30 wide, .022 thick, or, 24 wide, 1½ thick, 20 inches long Dennison gauge - Made in Switzerland
Nu Vigor Mainspring No. 1074 – for Seth Thomas 18-size Factory No. 729 – 50.80 centimeters long, 3.30 wide, .022 thick, or, 24 wide, 1½ thick, 20 inches long Dennison gauge - Made in Switzerland
Nu Vigor Mainspring Package No. 1075 – for Seth Thomas 18-size Factory No. 828 – 50.80 centimeters long, 2.90 wide, .22 thick, or, 20 wide, 2 thick, 20 inches long Dennison gauge - Made in Switzerland
Nu Vigor Mainspring No. 1075 – for Seth Thomas 18-size Factory No. 828 – 50.80 centimeters long, 2.90 wide, .22 thick, or, 20 wide, 2 thick, 20 inches long Dennison gauge - Made in Switzerland

Nu Vigor

Nu Vigor Mainspring Package No. 1072 – for Seth Thomas 18-size Factory No. 141 – 53.34 centimeters long, 3.30 wide, .022 thick, or, 24 wide, 2 thick, 21 inches long Dennison gauge - Made in Switzerland

Seth Thomas Models 2, 3, & 4 SECOND QUALITY

Nu Vigor Mainspring No. 1072 – for Seth Thomas 18-size Factory No. 141 – 53.34 centimeters long, 3.30 wide, .022 thick, or, 24 wide, 2 thick, 21 inches long Dennison gauge - Made in Switzerland

Nu Vigor Mainspring Package No. 1073 – for Seth Thomas 18-size Factory No. 536 – 53.98 centimeters long, 3.30 wide, .195 thick, or, 24 wide, 3¾ thick, 21¼ inches long Dennison gauge - Made in Switzerland

Seth Thomas Model 6 & 7

Model 5 ser#’s 300,000 to 350,000

Nu Vigor Mainspring No. 1073 – for Seth Thomas 18-size Factory No. 536 – 53.98 centimeters long, 3.30 wide, .195 thick, or, 24 wide, 3¾ thick, 21¼ inches long Dennison gauge - Made in Switzerland

Nu Vigor Mainspring Package No. 1074 – for Seth Thomas 18-size Factory No. 729 – 50.80 centimeters long, 3.30 wide, .22 thick, or, 24 wide, 1½ thick, 20 inches long Dennison gauge - Made in Switzerland

‍ ‍Seth Thomas Century Models 10 & 11

Nu Vigor Mainspring No. 1074 – for Seth Thomas 18-size Factory No. 729 – 50.80 centimeters long, 3.30 wide, .022 thick, or, 24 wide, 1½ thick, 20 inches long Dennison gauge - Made in Switzerland

Nu Vigor Mainspring Package No. 1075 – for Seth Thomas 18-size Factory No. 828 – 50.80 centimeters long, 2.90 wide, .22 thick, or, 20 wide, 2 thick, 20 inches long Dennison gauge - Made in Switzerland

‍ ‍Seth Thomas Century Models 12 & 13

Nu Vigor Mainspring No. 1075 – for Seth Thomas 18-size Factory No. 828 – 50.80 centimeters long, 2.90 wide, .22 thick, or, 20 wide, 2 thick, 20 inches long Dennison gauge - Made in Switzerland

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Sandsteel Mainspring Package No. 2106 – Seth Thomas 16-size, 2.40 millimeters wide, .022 thick, or, 15 wide, 2 thick Dennison gauge
Sandsteel Mainspring No. 2106 – Seth Thomas 16-size, 2.40 millimeters wide, .022 thick, or, 15 wide, 2 thick Dennison gauge
Sandsteel Mainspring Package No. 2521 – Seth Thomas 12-size, 2.00 millimeters wide, .20 thick, or, 11 wide, 3½ thick Dennison gauge
Sandsteel Mainspring No. 2521 – Seth Thomas 12-size, 2.00 millimeters wide, .20 thick, or, 11 wide, 3½ thick Dennison gauge

Sandsteel

Sandsteel Mainspring Package No. 2106 – Seth Thomas 16-size, 2.40 millimeters wide, .022 thick, or, 15 wide, 2 thick Dennison gauge

Seth Thomas 16-size Centennial Model 21

Sandsteel Mainspring No. 2106 – Seth Thomas 16-size, 2.40 millimeters wide, .022 thick, or, 15 wide, 2 thick Dennison gauge

Sandsteel Mainspring Package No. 2521 – Seth Thomas 12-size, 2.00 millimeters wide, .20 thick, or, 11 wide, 3½ thick Dennison gauge

Seth Thomas 12-size

Sandsteel Mainspring No. 2521 – Seth Thomas 12-size, 2.00 millimeters wide, .20 thick, or, 11 wide, 3½ thick Dennison gauge

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Unit Resilient Mainspring Package – for Seth Thomas 6-size Century .15 thick.
Unit Resilient Mainspring Package – for Seth Thomas 6-size Century .15 thick.

Unit Resilient

Unit Resilient Mainspring Package No. 1002 – for Seth Thomas 18-size Century .22 thick

Seth Thomas 18-size Century

Unit Resilient Mainspring No. 1002 – for Seth Thomas 18-size Century .22 thick

Unit Resilient Mainspring Package – for Seth Thomas 6-size Century .15 thick.

Seth Thomas 6-size Century Model 18

Unit Resilient Mainspring Package – for Seth Thomas 6-size Century .15 thick.

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U. S. R. Mainspring Package – for Seth Thomas 18-size Old Style No. 23
U. S. R. Mainspring Package – for Seth Thomas 18-size No. 536
U. S. R. Mainspring Package – for Seth Thomas 18-size No. 536
U. S. R. Mainspring Package – for Seth Thomas 12-size.
U. S. R. Mainspring Package – for Seth Thomas 12-size.

U.S.R.

U. S. R. Mainspring Package – for Seth Thomas 18-size Old Style No. 23 (by Ulysse Sandoz-Robert of La Chaux-de-Fonds, Switzerland).

Seth Thomas Model 1

U. S. R. Mainspring – for Seth Thomas 18-size Old Style No. 23

U. S. R. Mainspring Package – for Seth Thomas 18-size No. 536

Seth Thomas Model 6 & 7

Model 5 ser#’s 300,000 to 350,000

U. S. R. Mainspring Package – for Seth Thomas 18-size No. 536

U. S. R. Mainspring Package – for Seth Thomas 12-size.

Seth Thomas 12-size

U. S. R. Mainspring Package – for Seth Thomas 12-size.

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Additional Sources Consulted / Future Evidence Sought

Banner / Lapp & Flershem

Lapp & Flershem; Key to Discounts for Your 1900 Catalogue, Page 30; Published by Lapp & Flershem, Chicago, Illinois, U.S.A.; 1900.

Surviving Lapp & Flershem “Banner Main Springs” tins, included as examples of the branded mainspring line advertised in the 1900 Lapp & Flershem catalogue. These tins are not marked for Seth Thomas.

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Diamond / Benj. Allen & Company

Benj. Allen & Company; Illustrated Price List of Watch Materials, Tools and Jewelers’ Supplies, Page 258; Published by Benj. Allen & Company, Chicago, Illinois, U.S.A.; 1900.

This is the listing of the Benj. Allen & Co. Part No., 76, and price ($1.50) for the Seth Thomas Model 1 mainspring.

This is the listing of the Benj. Allen & Co. Part No., 149, and price ($1.50) for the Seth Thomas Model 3 mainspring.

This is the listing of the Benj. Allen & Co. Part No., 220, and price ($1.50) for the Seth Thomas Model 2 mainspring.

This is the listing of the Benj. Allen & Co. Part No., 271, and price ($1.50) for the Seth Thomas Model 4 mainspring.

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E. B. & Bro. / Emil Braude & Bro.

Emil Braude & Bro.; Supplement Five to Our 1903-1904 Catalogue, Page 3; Published by Emil Braude & Bro., Chicago, Illinois, U.S.A.; 1903.

See More Supplements of the 1903-1904Catalog

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E. & J. Swigart Company

The E. & J. Swigart Company; Illustrated Manual of American Watch Movements, Page 183 “SETH THOMAS and CENTURY”; Published by The E. & J. Swigart Company, Cincinnati, Ohio, U.S.A.; 1952.

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Liberty Bell / Henry Paulson & Co.

Henry Paulson & Company; Henry Paulson & Company Catalog, Front Cover; Published by Henry Paulson & Company, Chicago, Illinois, U.S.A.; 1918.

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O. N. & Co. / Oskamp, Nolting & Company

Oskamp, Nolting & Company; The Great American Jewelry Catalogue- 1905, Page 478; Published by Oskamp, Nolting & Company, Cincinnati, Ohio, U.S.A.; 1905.

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References/Bibliography