Wire welders

I have a Lincoln weld pak 100HD (yes the home depot one but it was free) and was wondering if there is any flux cored wire smaller than the .035 it comes with. Do I have to change the tip and sleeve if I go to the smaller wire?
The reason i'm asking is the bed of my truck has some holes in it from where someone has drilled into it to mount something many years ago. Is the .035 flux cored good enough for this or do I need to go smaller?

Im not sure on the lincoln but if you look at the feed roll and it has 2 diferent grooves then it should take 2 diferent spool sizes.My hobart is .035 and .023 You turn the feer roll over for the other side.Yes you do need to change to a smaller tip for smaller wire.The nozzle doesnt need changeing

Do they make flux core in that small of size? All I see on the miller manual is .030

Hopfully some one with more knowlege will chime in as im not sure.Iswitched to .023 solid core with a gas tri mix for body repair.This may help you.http://www.lincolnelectric.com/assets/servicenavigator-public/LINCOLN3/im546.pdf