The hole punch (which I used initially to cut through the blobs) is a boughten punch that is for a #2 grommet (Sailrite, etc.).
However, ultimately I decided that it would be better to completely remove the blobs, in which case I might not have needed the punch. Still it's probably useful to cut through them as a part of removing the rivet, and it does make a relatively neat hole (however the gelcoat is prone to chipping since it is over soft caulk).
