This is Ceramic In-Ear Earphone Shell for Sennheiser IE800 driver unit with MMCX (Shure spec) Connector
See reviews from Trustedreviews
What are the Sennheiser IE 800?
The Sennheiser IE 800 are some of the most expensive universal earphones you can get. They cost £600, making them terrifyingly pricey for most people.
They don’t have the usual sound we expect from a really high-end earphones, though. With some of the deepest bass we’ve heard in IEMs they’re surprise party monsters.