I think the one I pic'd is a 1/8", which works on most cars. A 3/16" works on later cars but can't fit in the spin pocket on a lot of older ones ... but it wears a lot slower and can cut more post heads. A 1/16 is much more costly and good for some early cars where the post head is down in a deep pocket. But they do burn out fast. A little 3-in-1 oil preserves the cutter and lets it cut 3 to 5 times as many posts, but the oil WILL go everywhere, and it means one more dip in the acetone before going into the polisher.

Home Depots have 'em ... but ya gotta read the cards because they're always on the wrong pegs ;-(

- E