For cleaning bolt threads, the bench grinder with a wire wheel is best. The hand drill with a wire wheel will jump all over the place. After a few restorations I must have cleaned hundreds of bolts on the bench grinder. The only regret is that I wish it had more power to keep it from stalling. It is a Craftsman 6", if I did it over I would go with an 8". My 2 cents.
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