An adapter for a Siedle intercom to allow a cheaper speaker to be used. Specifically, it's made for a Visaton 2899 (https://mouser.com/ProductDetail/Visaton/2899?qs=bT6MOr62zwLnQD85Rj62qg%3D%3D)

Compatibility with other speakers is probably pretty limited, as the adapter relies on the design of the speaker to secure it.

Be careful when removing supports, as the little knobs are prone to breaking. Luckily, only 3 are needed.