Wanting to use 4 bolts with rubber heads (instead of casters) to lift my #3 a bit from my table. Brought a caster to Home Depot but a 1/2 inch stainless nut seemed a bit too tight. Figured a 1/2 inch (diameter)stainless bolt would work, perhaps would be a bit loose. However, back home the bolt seats a short distance then gets too tight to finger thread into the legs. Are these standard threads? What size? Thanks in advance.