Many American antique clocks with open (not in a barrel) mainsprings use a “standard” mainspring of 3/4″ wide and approximately 18 thousands of an inch thick. There is a lot of variation in these springs between manufacturers, and across clocks made by the same manufacturer. I will comment more on these variations later.
In general, these clocks will work with thinner mainsprings if the pivots are polished and the necessary bushings installed properly. Also, some of these clocks show severe wear to the mainwheel teeth. Installing a thinner mainspring can reduce future wear.
Merritt’s Antiques has a mainspring specified as 3/4″ x .0165″ x 96″, part number P1496. Some of the springs in the first batch I received were about .0155 inches thick. They provide plenty of power for many 8-day American antique clocks, and have worked perfectly in the following applications so far:
- Ingraham oak kitchen clock, ca. 1880, for both time and strike.
- Ansonia oak kitchen clock, 4 pillar movement, strike side (this spring is also fine for the time side, as the original mainsprings are about the same thickness, in fact, even thinner springs would work).
- Waterbury oak kitchen clock steel plates, brass bushed, time and strike springs (this movement originally had thin mainsprings).
- Ansonia oak kitchen clock, 5 3/4 inch tall 5 pillar movement, time and strike springs
- Ingraham time only store regulator, deadbeat escapement, clock runs 15 days on one winding.
The mainsprings in this batch can be identified by being packaged in red, yellow and orange boxes.
In the Waterbury clock mentioned above (my job no. 4369), the new strike mainspring broke in September 2007. I replaced it with the same type of spring Sept. 28, 2007 (0.0155 inch thick).
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