The crank bolts are made of steel material, strong and durable. With plastic seal outside (no separate crank cap required). Fit for crank systems with ISIS inner bearing with M15 thread. Compatible with Bosch e-bike drives, compatible with Brose e-bike drives. Bicycle crank screw with screw lock (screw adhesive), protects against vibration loosening as well as against unwanted screw loosening and offers protection against corrosion. You will get 4 pieces of bicycle M15 crank screw. The size of the crank bolts is 21.6x20.6mm. Material Steel, Plastic Colour Black, Silver Size 21.6x20.6mm Thread length 13.1mm Type Crank Screw Brand Unbranded/Generic MPN Does not apply EAN Does not apply .