The Spare Clamp Arm Post is for BeadBuster XB-450i (and old XB-451, 452 & 454 PRO models). It allows for these tools to be used with ATV's with Reinforced Rims, which have a ‘Reinforcing Ring' (aka: Rock Ring). Reinforced Rims (not to be confused with Bead Locks) can be found on some OEM and aftermarket Baja racing wheels.