Here's my experience: The one-piece gudgeon is from Hobie Europe or somewhere (metric hole spacing?), so the instructions directed me to slightly enlarge the holes in the gudgeon to match those in the transom. If your existing transom holes and screws are stock (#12) and in good condition, then no tapping should be required for the existing holes. Of course, with the one-piece gudgeon, you will have a new pair of gudgeon holes per side, and to utilize them you'll need to tap the transom. I used a 1/4 inch tap (slightly larger than #12), and the heads on the 1/4 inch screws were indeed a little too large (had to file a little) as mentioned above. Drilling and tapping the new holes was easy, and I did not have to grind the castings. It was a snug fit, though. Finally, all-in-all I have been pleasantly surprised with the wear characteristics of the one-piece gudgeons as compared to the older, stainless ones. Hope this helps!

Jerome
Hobie 16 "RATTLE 'N HUM"
Clinton, Mississippi