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 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 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 Mainspring 2nd quality, as 20 inches long, .132 wide, .009 thick, or, 24 wide, 1¼ thick Dennison gauge.
Model 5 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 - 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 - 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 - 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 - 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 - Mainspring with patent brace, as 20 inches long, .116 wide, .009 thick, or, 20 wide, 1¼ thick, Dennison gauge.
Model 14 Mainspring with patent brace, as 17 inches long, .076 wide, .0065 thick, or, 10 wide, 4½ thick Dennison gauge.
Model 15 Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.
Model 16 Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.
Model 17 Mainspring with patent brace, as 17 inches long, .076 wide, .0075 thick, or, 10 wide, 3 thick Dennison gauge.
Model 18 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.
| Manufacturer | Number | ST Application | Factory No. | Length | Width | Thickness | Dennison |
|---|---|---|---|---|---|---|---|
| Black Shield | 4399 A | ST 12-size New Model | not stated | not stated | not stated | not stated | not stated |
| HR Alloy | SA 652 | ST 18-size | No. 536 T Brace | 21½ inches | 3.30 cm | 0.19 thick | 24 wide, 2 thick |
Black Shield
Black Shield No. 4399 A – Seth Thomas 12-size New Model
Charles Robert
Charles Robert No. 701 – Seth Thomas 18-size Factory No. 536, 3.30 centimeters wide, 0.185 thick, or, 24 wide, 4½ thick Dennison gauge
Charles Robert No. 705 – Seth Thomas 12-size .0205
E. & J. Swigart Co.
E. & J. Swigart Co. No. A 1175 – ST 18-size Factory No. 828, 20 wide, 1½ thick Dennison gauge
Etiquette Inc.
Etiquette Inc. No. 520 – ST 18-size Factory No. 536
The Fulton
The Fulton “Wine Color” – ST 18-size .019
HR Alloy
HR Alloy No. SA 652 – ST 18-size No. 536 T Brace, 21½ inches long, 3.30 centimeters wide, 0.19 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland
Marco
Marco No. 1001 – ST 18-size New Style Factory No. 536
Marco No. 1010 – ST 16-size New Style Factory No. ___ - Made in Switzerland
New Vigor
New Vigor No. 1072 – ST 18-size Factory No. 141 – 53.34 centimeters long, 3.30 wide, .022 thick, or, 24 wide, 2 thick Dennison gauge - Made in Switzerland
Sandsteel
Sandsteel No. 2106 – Seth Thomas 16-size, 2.40 centimeters wide, 0.022 thick, or, 15 wide, 2 thick Dennison gauge
Unit Resilient
Unit Resilient No. 1002 – ST 18-size Century .022
U.S.R.
U. S. R. – Seth Thomas 18-size Old Style No. 23