2-1/8" Diameter. For threaded dash air brake valves (threaded bendix type used from 90's through today). Made with a polished billet collar with the correct built in thread. Also features a set screw in the collar to align the knob with logos, etc. to keep them tight.
(5/8"-11 female threads)
Includes alignment set screw and allen wrench. Simple installation, thread your old ones off, thread the new ones on, Line up the logo or name and tighten the jam screw to lock it on. Thread-on style only.