Below you will find 2 different versions of our ferrous metal detecting magnetic Speed and Direction Sensors. The 37ADSD is a true 0 speed version that is sensitive to ferrous targets above and below the centerline. This version works better for targets that always have an edge in front of it, like a normal gear 4 to 32 pitch. If the target has long flat teeth (greater than 1/4"), or the edges of the targets are more than 3/4" apart, use the 37ADSDO. This version is almost 0 speed, and is sensitive to increasing and decreasing flux, like bringing a target closer to and farther from the sensing face. Click on the box that best fits your needs, and you will be brought to the electrical option choice page.