Haake key transfer systems are used to securely lock the keys of a machine. The secondary keys cannot be removed from the transfer system until the primary key is also present. Namely, the primary key must first be removed from a switching element, in order to subsequently release the secondary keys from the transfer system. Unlike the other Haake elements, a key transfer system is used when multiple secondary keys with the same encryption are desired. For example, to open several doors or hatches at the same time after switching off the machine. Key transfer systems are therefore an important link between switching elements and locking mechanisms.