I was looking at replacement drive rolls for my 221 Sti when I noticed that there are dual rolls offered for Power i-MIG series 230i, 253DPi, 275S, 275P, and PowerMTS series 221STi, 251Si, 252STi. "For use with "4 roll" system with 2 sets of drive rolls (1Drive+1Idler x2)". My model did not come with a dual roll feeder, but it would definitely be an upgrade since I can't gain any traction for a consistant and steady feed rate. I'm not familiar with features offered on the other models, but is the 4 roll system installed on other models?