I had the holes going through the R/H wing lower skin into the spar drilled to a 5/32”. I used #21 reamer to bring those holes to a #21 hole. Makes a very nice hole. I'll be drilling the other holes that need an A5 rivet using this method. First I noticed that on the inboard end I have an oval hole that looks to be an access panel. The drawings don't show this so I just sent an email to Zenith asking the question.