The RAP-S-KNOB5-4U consists of a 5/16"-18 female threaded security knob and key knob. The RAP-S-KNOB5-4U replaces all knobs on 1.5" diameter C size arms and mounts. The RAP-S-KNOB5-4U 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-KNOB5-4U is low in profile and only adds a small amount of additional bulk to your system when 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 comes at a very affordable price. The RAP-S-KNOB5-4U is the perfect accessory for keeping your mounted electronic device safe from theft and tampering.