Is there any type of printed matter that gives the correct size of mainsprings for American clock movements.

Hi Clifford,

If we are talking about out-of-the barrel mainsprings:
You can invest in books that reveal the original dimensions, or you can take the "close enough" approach. The former doesn't matter if you are buying a modern replacement. You are limited to what is for sale.

You can pretty much bet that an 8 day open mainspring is about 96 inches long. Now you need the width and thickness. (Thickness is also called "strength".) With luck, you have at least a piece of the old spring to measure. Check your catalogs for the closest match.

I was going to go into in-the-barrel springs, but I'll stop instead and ask a question. What sort of movement are we talking about, and what do you know about the old spring? That will help.

Best,
Tom

If you have kept a La Rose catalog,they used to have a spring section listing of what springs went into different clocks. I suspect is was just a ball park in some cases, but it was a start. I don't remember if they had barrel springs listed or not.

For this and other clock repair questions, I highly recommend this site by John Losch:
Articles on clockmaking and repair.

Best,
Tom