Headset - bike-vintage.com

Manufacturers

Information

Threaded Headsets
Size Steerer O.D.	Stem diameter Steerer I.D.	Crown race Inside diameter	Frame Cup Outside Diameter	Threads Per inch	Notes
BMX/O.P.C bikes	.833" (21.15 mm)	26.4 mm	32.7 mm	24	Used mainly on bicycles with one-piece cranks, also some early mountain bikes.
French 25 mm	22 mm	26.5 mm, 27.0 mm	30.2 mm	25.4 (1 mm)	Obsolete. French steerers usually have a flat filed on the back, rather than a grooved keyway as with other threaded systems.	Interchangeability note: These 5 sizes of forks and headsets all fit the same frames, since the head tube size is the same.
1" ISO Standard (25.4 mm)	7/8"(22.2 mm)	26.4 mm	30.2 mm	24	This is the standard 1" size.
1" Italian (25.4 mm)	7/8"(22.2 mm)	26.5 mm, 27.0 mm	30.2 mm	24	Obsolete. Threads are cut at 55 degrees, but ISO or J.I.S. headsets can be used.
1" J.I.S. (25.4 mm)	7/8"(22.2 mm)	27.0 mm	30.0 mm	24	Older or lower-quality bicycles from Asia
1" Raleigh (25.4 mm)	7/8"(22.2 mm)	26.4 mm	30.2 mm	26	Proprietary size used on Raleighs made in Nottingham, England
Austrian (26 mm)	22 mm	26.7 mm	30.8 mm	25.4 (1 mm)	Higher quality Austrian bikes use English/ISO
French Tandem 28 mm	22 mm			25.4 (1 mm)	Obsolete and rare.
1 1/8" (28.6 mm)	1" (25.4 mm)	30.0 mm	34.0 mm	26	"Oversized" (This size is more often used for threadless systems.)
1 1/4" (31.8 mm)	1 1/8" (28.6 mm)	33.0 mm	37.0 mm	26	Mainly used on tandems

Threadless Headsets
Size/Stem diameter Steerer O.D.	Crown race Inside diameter	Frame Cup Outside Diameter	Notes
BMX/	26.4 mm	32.7 mm	Used mainly on bicycles with one-piece cranks.
1" ISO Standard (25.4 mm)	26.4 mm	30.2 mm	This is the standard 1" size.
1 1/8" (28.6 mm)	30.0 mm	34.0 mm	Most newer mountain bikes use this size.
1 1/4" (31.8 mm)	33.0 mm	37.0 mm	Mainly used on tandems
1.5" (38.1 mm)	39.8 mm	49.6 mm	Proposed OnePointFive standard for downhill and freeride applications.