I have an 0 size Waltham Serial #16644987 in need of a mainspring. Would someone be able to tell me the part #? It is a model 1907, grade 165.
Many thanks!

I beleive that it is #2230.

Mike is correct "2230" but they are listed in four lengths;
8 inches long at .14 mm thick
9 inches long at .13 mm thick
9 1/2 inches long at .12 mm thick
10 inches at .11 thick

This spring is listed as being for size 0-3/0 so I would presume the longer length would be for "0" size.Only speculation on my part though.

Hmmm - my Waltham factory mainspring chart says that the #2230 mainspring is 12-3/4 to 15-3/8 inches long with a width of 2.05 mm to 2.10 mm. Thickness (strength) ranges from 0.11 mm to 0.14 mm.
In my 1924 Waltham material catalog they only list a 15"-long spring, so I would guess that the shorter one is later than your movement. Be sure to measure the old one (or use a depth guage) to know which width will fit the barrel.

[Width and thickness have been corrected in response to Kenny's post immediately below. Color my face red].

Jerry,
My info is from the "Swigart Manual". It lists the width on all four as 2.06 mms. You have your decimal misplaced on the widths. Would be 2.05 - 2.10.

Grant,
As Jerry says better measure each dimension.

Kenny - you are right, of course. I copied the numbers from the chart without thinking if they made sense. The columns were not labeled, but another version indicates the numbers are in "centimeters". I have corrected my post above to avoid confusing people more. The lengths I posted are still correct, with that column labeled "inches".

Thanks Gents. I'll measure!
Grant

Okay:
I measured it up, and here is what I found:
1-Length=15 inches
2-width=2mm
3-thinckness=.14mm
Given all the information above, can someone tell me how to/where to oder the correct spring from?
Thank you!
Grant

Grant,
Here are two links that carry #2230 but I can`t figure which one is correct?

DASHTO Mainsprings

S. LaRose

Brian C. might be a source also.