Fort knox for wheels. Tackling the perennial issue of wheel security, Delta Cycle high-grade locking Skewers and nuts will challenge even the most determined thieves. The patent pending knoxnut features a one-of-a-kind nut protected by a super tough free-floating outer ring, making it impossible to Release your wheel with anything other than the special key. Knoxnut key. The special forged key is lightweight and easy to carry. Use with regular 6mm Allen key to unlock. All keys are marked with a unique serial number. Knoxnut front skewer fits 130mm axles knoxnut rear skewer fits 168mm axles.