These adapt your Chris King Bottom Bracket to your crankset, and are required for use of your bottom bracket. If you&';re swapping cranks, you can keep your bottom bracket and just get an updated fit kit. If you have a Chris King Bottom Bracket in your cart, this fit kit will be discounted to 0$ when added to your cart! Fitment Guide #1 DUB A: For use with all SRAM DUB mountain crank fitments #3 ThreadFit 30: For use with ThreadFit(TM) 30, ThreadFit(TM) T47 30i, ThreadFit(TM) T47 30x #4 Bottom Bracket 24: For use with 24mm spindle cranks such as Shimano #6 GXP: For use with older style SRAM GXP cranks