Directional tread pattern with smooth center tread

Recommended for use with 10 or 11sp chain (10sp chain works on 9sp drivetrain)

30% lighter without sacrificing stiffness

These allen wrenches also have a convenient ball end for quick turns of a bolt

Special MTB gear teeth profile improves chain engagement and retention

Shimano UN55 English SQUARE-JIS 73x113mm Bottom Bracket Compatio_Enriched Directional tread pattern with smooth25% more durable than UN54 with alloy left hand cup Traditional square JIS 2 degree taper crank arm interface Offered in either English (BC1. 37 x 24tpi RH LH) or Italian (M36 x 24tpi RH RH) threads