This StairMaster StepMill 12-tooth Transmission Sprocket has a 5/8" inside diameter. It is designed to work with Stepmills including Nautilus SM916 and Stairmaster SM 916. Also works with Stairmaster 7000PT and SM5 150005. Compatible with OEM# SM23427. Buy more than three and save with our quantity discount program. See also our Sprocket Set Screw SML048