As I understand it, quill stems come in different sizes for the quills.
1 1/8":25.4mm
1: (7/8"):
22.2 (most modern stems)
22.0 (French Sizing. Motobecane, etc)
21.15 (Obsolete American Sizing)
Bar clamp sizes (road drop bars). See
Sheldon Brown for more notes.25.0 (French)
25.4 (ISO)
26.0 (Italian, quite common, modern?)
26.4 (old Cinelli)
31.8 (Road oversized (new))
So, for a non-French, non early American, 1" quill, go with a 22.2 quill size, and either 25.4 or 26.0 bar clamp size.