The 1A3 Tachometer Sending unit is designed to screw into the engine’s mechancial tachometer port (Lycoming/Continental style). Included is a .156 diameter tang along with a 6′ harness (other lengths available). Franklin engines require a different tang. The 1A3 TSU is designed to work with UMA TSU tachometers only. Optional equipment on the engine may complicate installation