Headset Cartridge Bearing Enduro ACB 3645 BOCC 30.2x41x6.5 mm 36ºx45º

Angular-contact headset bearing featuring anti-corrosion Black Oxide/Magnetite coated 52100 High-Carbon Chromium alloy races paired with grade 10 Balls. Black Oxide coating (BO CC) provides an extra level of corrosion resistance and extended worry-free performance

This size bearing is also known in the bike Industry by these part numbers:

IS41 standard
27287-1046-004
HSS0130K
TH-873E
MR-122

The Enduro line of angular-contact headset bearings are always engineered with the largest balls possible, feature dual-lip seals riding in a micro-groove (labyrinth) and are filled 90% with high pressure water proof grease for the ultimate protection against sweat and the elements. Enduro angular contact bearings (ACB) are designed so all balls are evenly engaged to spread the force over a larger surface area, decreasing friction, minimizing wear and maximizing life.

Static load - 935lbf / 4.15kN
Weight - 19.24g

If you are not sure what headset standard your bicycle has, please reference this guide:
https://www.parktool.com/en-us/blog/repair-help/headset-standards