Before you startGeneral guidance from our members' experience, checked against the sources listed at the foot of this page. Old bicycles vary, so check everything against your own bike. Brakes, steering, wheels and tyres are safety-critical: if you're not sure, have a qualified mechanic do or check the work. Any work you do is at your own risk. See our terms.
| 1in threaded standard | Steerer thread (tpi) | Crown race seat | Frame cup outside diameter | Steerer diameter |
|---|---|---|---|---|
| ISO (the standard 1in size) | 24 | 26.4mm | 30.2mm | 25.4mm |
| JIS (Japanese) | 24 | 27.0mm | 30.0mm | 25.4mm |
| Italian | 24 | 26.5 or 27.0mm | 30.2mm | 25.4mm |
| French | 25.4 (1mm pitch) | 26.5 or 27.0mm | 30.2mm | 25.0mm |
| Raleigh (Nottingham-made) | 26 | 27.0mm | 30.0mm | 25.4mm |
Figures from Sheldon Brown's headset crib sheet, which also lists a 1¼in size used mainly on tandems. Measure the steerer and the old cups with calipers, or take the old headset to a shop to match.
Service and adjustment
- Test for playHold the front brake on and rock the bike back and forth. A clunk usually means the headset is loose.
- Strip itUndo the locknut and top race. Put a cloth under the head tube to catch loose balls.
- Inspect the racesA row of little dents worn into a race is called brinelling. It causes 'indexed steering', where the bars stick in the straight-ahead position. Badly brinelled races mean a new headset.
- Clean and greaseMost headsets use 5/32in or 3/16in balls. Swapping a ball retainer for loose balls of the same size can help a slightly worn headset.
- AdjustSheldon Brown's method: tighten the adjustable race by hand until the bearings just begin to bind, then back off about an eighth of a turn and lock it. You want free rotation with no play.
Don't ride with a loose headsetPlay damages the races quickly and affects handling.
Sources
Checked 19 October 2026. Method tips without a source are our members' experience.