Drive Cables for Mechanical Tachometers
Different tachometer manufacturers have used different end configurations on their drive cables:
Smiths Input: Tachometer drives (driven by the cam, oil pump, or crankshaft) with a Smiths drive have a special thread approximately 1/2" diameter and accept a flat blade-type drive dog on the cable.
0.104" Distributor Drive: Some distributors have a 7/8-20 thread and accept a 0.104" square drive cable.
0.187" Tang, 7/8-18: This drive has a 7/8-18 thread and accepts a 0.187" diameter cable with a small tang on one side of the drive cable.
Jones Output: Jones tachometers have a 7/8-20 thread and accept a heavy-duty SAE square drive on the end of the cable.
Smiths Output: Smiths tachometers have a special thread approximately 1/2" in diameter and accept a square drive cable.
Stewart-Warner Output: Stewart-Warner tachometers have a 5/8-18 thread.