What is the size of a #4 grommet? Greg H. January 06, 2020 19:16 The #4 grommets have an inner diameter of 7/16", and an outer diameter of 9/16". Related articles Will the Frogger Grommet Press hold different size grommets? Day 1 with your vinyl cutter Which tape is best for Oracal 631? Installing new fonts Forever Paper Comments 0 comments Please sign in to leave a comment.