1 truthtellerspook 5 years ago Piece of paper over f-hole, rubbed with side of pencil lead, provides pattern. Cut. Place over foam (the example in pics, flip flop foam), outline with white chalk. Cut from top at angle inward with exacto knife. Drop right in. Push a bit, seal. Just a tad over-sized at the top, tops ride just above the guitar, easy to take out. Consider chemical compatibility of foam material to guitar finish. Poly very forgiving; lacquer can be less so.