Used on a single-cylinder engine as it is difficult and expensive to find a good tachometer for a cylinder. I've tried these mini inductive tachometers that have the wire wrapped around the spark plug wire. They are unreliable and should not be installed. That works great. I installed at the end of the crank with a bolt and a couple of washers. Once you are sure the magnet is on the correct side of the cartridge, sand down the slot in the magnet discs and use some epoxy for extra protection. I had to make a bracket to mount the sensor (not a big problem). In fact, it reads RPM changes faster and more accurately than those little mini speedometers. I will be installing another one on my other tractor this fall.