Zenith 28G throttle disc  

As used in:

Numerous tractors, stationary engines, etc:

Ferguson Tractor TVO Petrol and Lamp Oil 1954-55
Ferguson Tractor petrol and kerosene engine 85mm bore: 1955-56
Ferguson Tractor petrol and kerosene engine 87mm bore: 1956-63
Massey Ferguson Tractor MF, FE35, 130,135, 140, 35X, TEP20 petrol engine: 1961-65
Massey Ferguson LO and TVO 87mm Bore 1965-67 
Ronaldson & Tippet Wisconsin AENLD & VH4D: 1958-63
Southern Cross (Toowoomba Foundry Ltd.) Mk EY-D petrol engine 1961

Link to 28G throttle shaft here 015803