I think he was asking about the throw bar, which connects the 2 switch points, not the throw mechanism.
If it's outside, black UV resistant plastic is best. You can buy the ones from Aristo, but unfortunately, that is the only part of an Aristo switch that is not UV resistant.
Most black plastics will work better than something clear, since the UV rays cannot penetrate the outer layer of the plastic. Black nylon might be best.
Regards, Greg