Material doesn't really matter. Do use a lock washer w/internal teeth.
Edit: Considering your application, use stainless - with a drop of boelube on the screw threads. The switch terminals are tin/phosphor flashed over bronze (I think...look at the thread color to verify).
Material doesn't really matter. Do use a lock washer w/internal teeth.
Edit: Considering your application, use stainless - with a drop of boelube on the screw threads. The switch terminals are tin/phosphor flashed over bronze (I think...look at the thread color to verify).