I'm thinking I need at least a 1/4 inch. The dust cover is 7/8 inch. I think 1/2 inch would work. I don't think I could beat it down that much with a hammer. It looks like the inside diameter that goes inside the spindle is 2 inches if I could find one that is shorter.
How much shorter do the dust caps need to be? You can hit the dust cap with a BFH to get some clearance, as long as the middle of the cap doesn't make contact with the end of the spindle.
