The RAM locking knob, includes a brass 5/16"-18 thread, for 1.5" socket arms; this allowing 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.

Material: 
Powder Coated Marine Grade Aluminum 

Ball Size: 
1.5" Rubber Ball Size 

Note: 
The "U" in the part number reflects product packaged in poly bag.