Since I'm an electrican,I have a set of Klein hole punches,1/2 to 2 1/2", they are perfect for clean smooth round holes in almost any thickness metal,just drill 1 hole in the middle,insert the bolt& bearing,and the cutting die screws onto the threaded bolt from the other side,turn bolt with wrench till it pops out,Perfect! no sharp edges,paint loss,or distorted metal.Home Depot and a few hardware stores have them.