RAM Mixed Combination Pin-Lock Security Knob and Key Knob for 1.5" Dia C Size ArmsThe RAP S KNOB5U consists of a 5 16" 18 female threaded security knob and key knob. The RAP S KNOB5U replaces all knobs on 1. 5" diameter C size arms and mounts. The RAP S KNOB5U offers the ideal amount of leverage to properly tighten your mount to prevent slippage in heavy chop or in extreme vibration environments. With an emphasis on aesthetics and function, the RAP S KNOB5U is low in profile and only adds a small amount of additional bulk to your