Vintage Stem and Handlebar Sizes

Sheldon Brown’s Bicycle Handlebar and Stem Dimension

Handlebar dimensions
Stem Clamp Size		Grip Area Size		Application
22.2 mm	7/8″	22.2 mm	7/8″	Steel bars. Mainly BMX, older Mountain bike bars.
23.8 mm	15/16″	22.2 mm	7/8″	Obsolete British size for steel handlebars, common on older 3-speeds. This size was also used for older British steel drop bars.
25 mm		23.5 mm		Obsolete French size.
25.4 mm	1″	22.2 mm	7/8″	Standard I.S.O. size, used on the vast majority of newer bicycles with upright handlebars. This size was formerly common for steel drop bars.
25.4 mm	1″	23.8 mm	15/16″	Standard I.S.O. size, used on most bicycles with drop handlebars. Also used on older British aluminium upright handlebars.
25.8 mm		23.8 mm	15/16″	Unofficial in-between size used by some Italian handlebar makers for handlebars designed to be usable in either ISO (25.4) or Italian (26.0) size stems.
26.0 mm		23.8 mm	15/16″	Italian standard for drop bars, other bars made to fit Italian stems and some high-end aftermarket drop bars. This is sometimes incorrectly called “road” size.
26.4 mm		23.8 mm	15/16″	Older Cinelli and Cinelli copies. Cinelli changed over to 26.0 mm in 1998.
27 mm		23.8 mm	15/16″	Titan (obsolete).
31.8 mm	1 1/4″	23.8 mm	15/16″	Road oversized.