This is a bag of 10 genuine Sennheiser replacement ear adapters in size S, black (Sennheiser spare-part article 506401). Ear adapters are the soft tips that fit over the sound nozzle of an in-ear earpiece and sit in the ear canal; they seal the ear so that bass response and isolation from outside noise are correct, and they hold the earpiece securely in place. They wear out, harden, split or get lost with regular use, and for hygiene they should be replaced when an earpiece is passed from one user to another, which is why AV rental companies, broadcasters, theatres and churches using shared in-ear monitoring or listening systems keep spare bags on hand. Size S suits smaller ear canals; Sennheiser also makes the same adapter in other sizes (S, M and L), so a mixed stock lets each wearer get a comfortable seal. Sennheiser's spare-parts catalogue lists this part by number but does not publish a compatibility list, so check that it matches the adapters already fitted to your Sennheiser earpieces before ordering. The pack contains 10 adapters.