Ram Mount Locking Knob with 1/4-Inch-20 Brass Hole for B Size Arms (Black) Includes a brass 1/4"-20 thread, for 1" (B size) socket arms Allows you to disengage the screwing of the knob Once you have set your mount in the location you need, you can lock it in place and feel safe that your mounted device will stay right where you left it Powder Coated Marine Grade Aluminum