The right key.
Chris King's new modular Bottom Bracket system is smart, but it leaves you needing to search for the right conversion kit for your bike. No problem. For riders who are running mountain bike cranks with a 24mm spindle, such as certain Shimano, FSA, Gravity, Race Face, and Surly cranks, and your bike has an 83mm-wide BB shell, you're going to want Chris King Bottom Bracket Conversion Kit #14. The Kit slips onto the crank's spindle and then into the Chris King ThreadFit 24 Bottom Bracket on your bike. If you have any more questions about the system or which CK conversion kit to use, please let us know and we'll help you out.