Yikes,

Hamilton 986/987's are a lot easier... This pocket watch stuff is bigger but a lot less forgiving.

I got the main spring out of the other movement and to my dismay, there are three replacement choices available, non of which seem to match the one in my hand.

The one that came out has a folded back flag at the barrel. The replacements available are T, H, M and hole.

Pictures of M and H are not available. I'm inclined to think the nub on the barrel should fit the hole type spring... but that choice is radically different than the one that came out.

Any suggestions?

R/Pault

Paul, I believe what you need is a Howard #552 hole end mainspring.