The RAP-S-KNOB5U consists of a 5/16"-18 female threaded security knob and key knob. It 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 extreme vibration environments. With an emphasis on aesthetics and function, it is low in profile and adds only a small amount of additional bulk to your system compared to the standard knob included. At a fraction of the cost of currently available keyed locking knobs, the additional peace of mind and tamper resistance come at a very affordable price. The RAP-S-KNOB5U is the perfect accessory for keeping your mounted electronic device safe from theft and tampering.