This is a SureFit dome set for GN Resound hearing aids with 10pcs of different sizes, which are Small-5mm, Medium-8mm, and Large-10mm. You could find the other variations in different combinations in our store page. These domes could be used with ReSound LiNX2, LiNX3D, LiNX Quattro and ENYA behind the ear models (both RIC and open fit tubing BTEs) hearing aids, or some other brand hearing aids. These are NOT suitable for some RIC models with large square receiver end. We suggest you to start with the mixed set with 3 different sizes in our store, which will help you find the most suitable size for your ear canal. If the dome is too big, your ear canal will feel pressure and will not be comfortable. If the dome is too small, the sound will be leaked and you will hear a terrible squealing. So it's important to choose your suitable size carefully in advance. If you already know which size will be suitable for you, then please directly purchase a set with your suitable size. Hope you enjoy our products and service. We sincerely look forward to your good reviews.