redmadder,
Sigh .... there's the rub, most of the Singer parts are made in China. They probably took the "inch" measurements and rounded them up to the next largest "millimeter". That's fine if you're building a B-29 Super Fort by reverse engineering like the Russians did during WW II, but for parts used in "inch" made machines it doesn't always work.
I'd suggest returning them to where ever you bought them.
Joe