This is a replacement part for my uncle's treadmill. There are 2 parts and they both should fit together snugly. His old timing wheel was made of cheap abs and cracked in multiple places. He couldn't find a replacment part so I decided to design him one. The purpose of the wheel is to relay the speed back to the treadmill. A light or laser shines through the holes at a sensor and depending on how many times the light or laser comes into contact with the sensor it calculates the speed. It should be mounted on the treadmill bar with some glue or epoxy of some sort, since it's a little bit bigger than the bar and isn't meant to rely on friction mount.