Original Mainspring Dimensions -HAC W77 Movement


Registered User
Hi All, Could anyone please advise what the original dimensions were for the mainsprings fitted to these movements in the Going and Strike trains at the time of manufacture ? The movement is marked as follows:

W77 over
"Crossed arrows", ie 'HAC', bottom left hand side of rear plate.

187/35 over
83, top left hand side of the rear plate,

345, (date code ?), top right hand side of rear plate.

Movement is Time and strike, only.

Many thanks in advance,

Willie X

Registered User
Feb 9, 2008
Well, I can give you some tips to go on.
Width is a given, 1mm less than the space available. Strength is the big question mark. On German clocks the strike spring is often thicker than the time spring by 1 to 3 thou. Once the strength/thickness is chosen, the optimum length can be calculated.

Do you have any parts of the old springs, this would help a lot. At least you would have some reference. If not, a good guess (or starting point) would be 15 thou for the time and 17 thou for the strike. The calculation will yield the correct lengths for the respective barrells. Assuming the barrels are the same size the time spring will probably be about 10" longer that the thicker strike spring. Willie X


Registered User
Hi Willie X,

Many thanks' for the response, much appreciated.

Unfortunately, there where no springs with the Movement to work from. I recall that what is usually found in the USA movements on the strike side is: 0.45mm x 17mm x the length needed as calculated. I would think the 0.45mm / 18 thou would be too strong for the Going train ?

Kind Regards,
Our 2021 National Meeting in Hampton Roads Virginia
Topic related ad experiment
Know Your NAWCC Forums Rules!

Find member

Forum statistics

Latest member
Encyclopedia Pages
Total wiki contributions
Last edit
How to wire a 24 volt secondary for a 12 volt ITR/IBM Master clock system by Toughtool