WARNING
THESE UNITS ARE NOT A SAFETY CLUTCH!
They prevent the tractor PTO and transmission being driven by implements on the over-run ie. inability to stop single clutch tractors such as the Ferguson Te20, TO20, MF35 single, Ford 8N, 9N, 2N when a Rotary Cutter IS attached.
No protection under load hence normally used in conjunction with a separate clutch.
