I need to replace the Strike side mainspring on a Pequegnat Greacin mantle clock. I measure the width at 16mm and the thickness at .40mm. How can I determine the length? I am reluctant to unwind it and stretch it out as I can see where the spring is broken almost all the way across the width and do not want it to bite me.

John, You have to take it out sometime anyway, so might as well put your face mask and gloves on and get out the spring winder. Is it in a barrel or is it an open spring?

Curly

Thanks for responding Curly: The spring is not in a barrel. I can remove the spring from the wheel without stretching it out. I was hoping there was a table or a spec by clock maker somewhere.

I was able to finish the break in the spring and measure the 2 pieces. Thanks for your help.