Middle doors can be many different keys, but let and take them age-wise from behind.
Old doors from 1940-ca 1970
For these doors, it is usually the Danziger key that is used, but it can also be a Rex key.
You can see a form on the Danziger key where you can lure the profile in the lock case.
Old Ruko middle door locks = 1583 Multi key
Rex Amca locks (also called 333) = REX 3B key or multi key 1583
REX 48 Lock cases (also called Rex 22) = REX 3 B Key or Multi-key 1583
414 lock case which had flat keys and could be turned = 414 The key
2214 lock cases = 2214 key
Virtually all newer intermediate doors are fitted with:
2014 Lock cases = 2014 The key