This is an amazing hold down device that actually rolls when you feed your stock. Each set of Safety Rollers comes complete and ready to install on your fence or fixture. Yellow rollers rotate in a clockwise direction and will not rotate counter-clockwise preventing kickback on your table saw or router table. Green rollers rotate in either direction so they are great for shapers or radial arm saws where they act as a hold-down, not as an anti-kickback device. Rather than permanently mounting the Safety Rollers to your machinery, choose the optional Safety Roller Mounting Track to move your Safety Rollers from one machine to another.