Quote Originally Posted by azsprint6 View Post
Being new to this I'm probably looking at this a different or wrong way. It seems like the wire size should be the same as the tip. There is enough clearance between the 2 for easy slippage and it's called a (contact) tip so it can charge the wire. It just seems like a .010 larger tip then wire may cause a problem. I'm probably off base here but .035 aluminum wire and .035 copper tip seem fine for me so far. These pics are my rookie welds, the one on the right is cold and the left one is preheated to 225 degrees without changing the settings. The part is over 1/2" thick.
One size over or drilling .01 over is common and recommended by many. The wire is trying to curl pretty hard from the small diameter of the roll so it makes good contact even with the oversize tip. I do the same for flux core steel wire to prevent feeding problems.