From the Manufacturer
Because every ear is different, Shure sound-isolating earphones come with a broad assortment of sleeves to ensure a personalized fit, as well as proper sound isolation. This pack includes 10 flexible, reusable sleeves that fit comfortably in the ear and are easy to insert. The flex sleeves are sized medium for people with mid-sized ear canals, so choose carefully for the best possible fit (Shure also sells small and large sleeves). They're designed specifically for use with the Shure E1c, E3c, and E5c sound-isolating earphones.
Product Description
Because every ear is different, Shure sound isolating earphones come with a broad assortment of sleeves to ensure a personalized fit, as well as to ensure proper sound isolation. These flexible reusable sleeves fit comfortably in the ear and allow for ease of insertion. Medium size - choose carefully for the best personal fit. For use with the E1c, E3c and E5c Shure Sound-Isolating earphones.