Hi Paul, I don't know what you call it was a wheel that was divided with slits and a magnet device that went on ether side of the wheel? but some times it gets grease on the sensor and won't work so I have to clean it with a cotton swab. I did just about every mod I could find on the internet to this lathe HF 9x20 . it has worked over ten years with out any problems it just keeps going and going. I am sure you have had better equipment to play with ?