Mainsprings for American 8 Day Clocks

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.

Box containing Merritt’s P1496 Thin Mainsprings

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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  1. I am looking for a spring drum with a spring already on it. I can’t find one anywhere. It is for a Sessions movement. Could you help? I find lots of springs but no wheels attached. I need both. If you could help, I’d be much appreciated. Thank you. Yours truly Emmanuel

  2. While dis-assembling a waterbury kitchen clock movement, I was talking to my husband and not paying attention, end result is I have two different sized main springs, and don’t know which went to what is heavier, can I assume this went to the strike side safely? I know, lesson learned! Thanks for any help

  3. I have a mantel self-Thomas clock. The 8 day main spring broke. It’s in a brass chamber with gears on the bottom part. It has a number #20 at the top.
    On the time piece it says.”Made in West Germany for Self-Thomas”…. How can I get this main spring?

  4. Hi Dan,

    First, don’t use the 0.18 inch thick mainspring – it is too strong and will cause mainwheel tooth wear. Use 0.0165 inch thick springs as discussed in the postings in this topic. Suppliers are given there, also see the “Clock Parts Links” in the right sidebar for clock parts suppliers.

  5. Hello, Bill.

    I am looking for a “mainsprings for wall clocks – for 8 days – loop end – size: 3/4″ x 0.18″ x 96”. Do you have it?

    Daniel Rocha

  6. Thanks for the reply. This is indeed the quarter strike movement. Both springs appear to be the same length.

  7. Hi Dave,

    The original mainspring for most No. 89 movements are 108″ long. The 89L movement might have had a longer strike spring, if this is the quarter strike movement. You did the correct thing by keeping the longer thinner springs.

  8. Hi Bill,
    I was given a pair of Seth Thomas mantel clocks for Christmas from a friend, one working, one not. I disassembled cleaned and reassembled the non-working one (has an 89L movement in it, bim-bam rods) and now it works great.

    When I bought the supplies (book, oil, mainspring letdown tool) I also bought a pair of mainsprings just in case. They were 3/4″ x 0.0175″ x 96″ from Timesavers.

    I didn’t use them because the originals (they’re stamped ST on the loop) appeared okay when removed and cleaned. The originals measured 0.0155″ thick though and when coiled next to the replacement, seems to have almost half again the number of turns.

    A lot of what I’ve read is that 3/4″ x 0.018″ x 96″ is common for 8 day American clocks but thinner should be used. What about longer springs?

    What do you think I have in this clock? Did Seth Thomas put longer than 96″ springs in their 89 movements?

    (just getting into this as a hobby)

  9. Were can I buy these springs for a Waterbury Clock similar of mencioned?

    And the price for 2 springs?

    Can you send it to Portugal?
    Wich will be the dispache price to Portugal?

    Thank you

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