Etymotic Research ER38-18 3-Flange Replacement Eartips - 10 Pack - Gray Package of 10 eartips Ear canal opening 8-13mm Designed for use with ER4 series, HF series, etyBLU2, Ety-Com, MusicPro, Gunsport Pro, EB-15 BlastPlug, and HD15-High Definition Electronic Earplugs.