This listing is for 2 retention locks. These will fit Resound One, Omnia and Jabra Enhance MEDIUM power speakers. These are for Surefit 3 receivers. The design helps keep the hearing aid speakers firmly in the canal while talking and chewing and during most physical activity. These locks can wear out over time. It is recommended to replace them every 6-8months. There are 3 sizes: Low Power (L) Medium Power (M) High Power (H) We have listings for all 3 sizes! On the tip of the hearing aid speaker you will the find the letter that corresponds to the power level of your speaker.