I figured out that instead of drilling holes, I could just use strong two-sided tape to attach the thumb rest into pick guard. Anyone thinking about it, I can save you from the trouble. This thumb rest is hollow, thus there is no surface on the backside to attach glue or two-sided tape for attaching the thumb rest without drilling holes. As for the quality, it's just a cheap piece of plastic with two screws for 9EUR. Don't expect anything better.