Trek lower headset bearing, 440C stainless steel used in many Madone, Domane, Emonda, Crockett and Cronus frames.

Dimensions: 40mm ID x 51mm OD x 6.5mm Wide. 36-degree x 36-degree design.

440C stainless steel balls and races provide long life and superior corrosion resistance in applications and environments that may be less than ideal. 440C has the highest strength, hardness, and wear resistance of all the standard 440-series stainless alloys with high carbon content.

Our part number: ACB6808SS

Replaces Trek part numbers W540243, 290413, and 417578

Compatible with Madone frames 2010 and later; all Emonda frames; many Fisher Cronus Ultimate frames; many Crocket and Boone frames.