Headset Bearing Measuring Guide
Headset Bearing Measuring Guide
Not sure which headset bearing you need? Print the guide, lay your old bearing on the to-scale rings and narrow it down to a reference number in a couple of minutes.
6 pages · A4 · print at 100% / Actual size, not "Fit to page"
This is a rough guide — confirm with digital callipers
Use the sheet to shortlist your bearing quickly, then check the inner diameter (ID), outer diameter (OD) and height with callipers before you order.
5 measurements identify any headset bearing
Inner diameter, outer diameter and thickness (height) in millimetres, plus the chamfer angle on both sides. Every bearing in our guide is listed in this format, for example:
#3 30.2 × 41 × 6.5mm · 36° × 45°
Missing one of the five is the most common reason people order the wrong bearing.
STEP 1 / 7
How to measure
STEP 1 — Check your print scale
Hold a ruler against the 100mm line on page 1.
No ruler? A bank card's long edge is 85.6mm and should end on the 85.6 mark.
Tip: always print at 100% / Actual size, never "Fit to page".
STEP 2 — Clean the old bearing
Wipe off dirt, grease and corrosion — they all add size.
STEP 3 — Match the outer diameter
Lay the bearing flat on the rings (pages 2–4).
The outer edge should sit on the solid outer line.
STEP 4 — Match the inner diameter
The dashed inner circle should line up with the bearing's bore all the way round.
STEP 5 — Check the thickness
Stand the bearing on its edge against the height gauge (5.5–8mm) and find the bar it matches.
STEP 6 — Check both chamfer angles
Use the bank card test or the cut-out gauges (page 6): push the bearing onto the 36°/45° points to check the bore, then sit it in the 36°/45° notches to check the outer race.
Check both sides — they aren't always the same.
STEP 7 — Confirm & order
Shortlist the closest reference, then confirm all five with digital callipers: ID × OD × thickness × angle × angle.
Chamfer angles: 36° or 45°?
Most headset bearings have an angled edge (chamfer) on the inner and outer races. It locates the bearing in the headset cup and against the crown race / compression ring. You'll usually find one of three:
The angle isn't always the same on both sides, so check each one.
The bank card test
A bank card has a perfect 90° corner, so each edge sits at 45° when you push the corner straight into the bore. Push it in and look at where the card meets the chamfer on both sides:
Turn the bearing over and repeat for the other side.
Cut-out angle gauges
A card with a 45° point at one end and a 36° point at the other. Push the bearing down onto a point — if the bore chamfer sits flush on both sides of the point, that's your angle. If it rocks or only touches the tip, try the other end.
A card with a 45° and a 36° V-notch. Lay the bearing flat in a notch, outer edge down — if the outer chamfer sits flush on both sides of the notch, that's your angle.
Page 6 of the guide has both gauges true to scale. Print at 100%, check the 50mm scale line, glue the page to stiff card (a cereal box is perfect) and cut them out.
Get the gauges (PDF)Caged bearings
Caged (loose-ball) bearings don't have a ring to overlay, so identify them by size and ball count.
20 × 5/32" balls
26 × 5/32" balls
15 × 1/4" balls
Peace of mind if it doesn't fit
Every UK headset bearing order includes a freepost returns envelope and an exchange form. If something doesn't fit, tick the size you need, post it back and we'll swap it.
Ready to measure?
Download the free guide, or browse headset bearings by bike. Still stuck? Message us on WhatsApp with your measurements and we'll match it for you.
