Someone asked me an interesting question today that I'm not qualified to answer since I'm primarily a wristwatch guy. Do all three 10-size Hamilton movements -- grade 917, 921, and 923 -- use the same pallet fork and escape wheel? I'm guessing that they would, aren't these different only in number of jewels and fineness of finish? Or are they like the 979/987 wristwatch movements, with some parts that are similar but not completely interchangeable?

no they are different if meomry servies me right the 917 and 921 use the same pallet fork .i think the escape wheel is the same but the escape wheel pinion on the 917 is a straight pivot and the 921 is conical pivots,..

the 923 uses a different pallet fork and escape wheel than does the 917 or 921 grades..

If i am wrong someone correct me but i think i am right.

I should have thought to dig through my reference books... I just pulled out the 1952 Swigart catalog. Samie is right on the money. Swigart shows the 917 and 921 use the same pallet fork, but the 923 is a different part number. All three use different escape wheels. Case closed!