Choose from thousands of styles for your thread on style Tractor Trailer dash knobs. Add Tractor Trailer engraving or custom engraving options. All of our 2-1/8 and 2-1/4" style knobs are available as brake knobs and listed under Semi Truck > Brake Knobs. All options are not listed here. Contact us for more details. All sold each. Mix and match any way you like. 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. Other options upcoming.