The 2" locking hitch pin allows you to lock the rack to vehicle. 206 - 308 Keys (Side Mount / Round Locking Head): Fits all 2" Sport Rider SE racks and 2" Road Runner racks 2 keys included Locking hitch pin diameter: 5/8" Length with the locking cylinder installed: 3-1/2" (90mm) Length without the locking cylinder installed: 4-3/4" (120mm) 105 - 107 Keys (In-Line / Rectangular Locking Head): Fits all 2" Sport Rider SE racks and 2" Road Runner racks 2 keys included Locking hitch pin diameter: 5/8" Length with the locking cylinder installed: 3-3/4" (95mm) Length without the locking cylinder installed: 4-3/4" (120mm)