This was the original thinking from Walt (Hombre): The standard TPS is a poor fit against the throttle body. Consequently when tightened with the setscrew, a stress is applied to this extremely sensitive potentiometer. IMO, this has been causing the frequent failures. The shim keeps the TPS "square" against TB, alleviating that stress... and so far keeping mine from failing
The failures are probably related to over torquing from the recommended 3.5nm. I doubt even Triumph dealers use a torque wrench on the TPS... its too **** sensitive. The critical dimension is the thickness of your shim stock. If you look closely at the TPS against the throttle body, you will see that the TB is not flush against the TPS where the screw mounts. That gap causes TPS to "cock" when torqued. The .010" shim fills that slim gap.
Shim is cut from .010" aluminium. Note that one side of "circle" is flat to fit TB.