most are 1/8 i found , just take it off and take it with you , just a snug fit and as short as you can find so they dont foul anything under the cowelling .
drill out old rivets and test fit , they wont worry . another way id drill out the rivet be sure not to enlarge the hole and test a drill bit in the remains then ya cant get a more accurate fit wink . old tricks still the best ones