Home mechanics and workshops replacing a worn MR031 (37 x 48.9 x 6.5 mm, 36/45) headset bearing.
The BlackBearing C100 is a replacement headset bearing measuring 37 x 48.9 x 6.5 mm with 36/45° angles. It's the size known internationally as MR031, found in some 1-3/8 inch headsets, including those fitted to certain Cervélo and Factor bikes.
It's an angular contact bearing built for steering loads, with SAE52100 chrome steel balls and races, headset-specific seals and quality grease. BlackBearing is a French company that specialises in bike bearings and makes more than 50 headset sizes.
A worn headset bearing shows up as notchy steering, a knock under braking or a creak when you stand up. Swapping the bearing alone is often all it takes to make the front end feel smooth and tight again.
MR031 size
37 x 48.9 x 6.5 mm with 36/45° angles.
Angular contact
Built for the loads a headset sees.
Chrome steel
SAE52100 balls and races.
Sealed and greased
Headset-specific seals, ready to fit.
Bearing
In the box
Angular contact design
Headset bearings carry loads at an angle, so this bearing uses oblique contact to handle steering and braking forces through the fork.
Great for
Maybe not for
All four numbers must match: 37 mm inside, 48.9 mm outside, 6.5 mm tall, 36° and 45° chamfers. Check the markings on your old bearing or your frame's service manual. Sold individually, so order two if you're doing a top and bottom that share this size.
Get the angles the right way up
A 36/45 bearing only fits correctly one way round, because each side has a different chamfer. Note which way the old one faces before you remove it, and fit the new one the same way.
Internal routing
On many modern road bikes the brake hoses run through the headset, so a bearing swap can mean disconnecting hoses and bleeding brakes. If that's your bike, we're happy to take care of it in the workshop.
Bearings made for bikes.
BlackBearing is a French company that specialises in bearings and parts for cycling, supplying both bike brands and workshops.
Its headset range covers more than 50 sizes for 1 inch, 1-1/8, 1-1/4, 1-1/2 inch and Cannondale steerers.
