On the 1987 BMW 325, the front brake hoses that go to the wheels are rubber so that they can flex as the wheels move and swivel.  The hoses attach to metal tubing that runs, presumably, to the ABS unit.

For each front wheel, the attachment point is a platform attached to the body, under the front wheel-well.  The metal tubing comes in from the bottom and the rubber comes in from the top (as I recall; it might be the other way around).

A spring-loaded clip shaped like an upside down “U” is to be placed onto the platform.  Both the clip and the platform have a hole through them, so that the tube and hose can be shoved through so as to connect at the clip.

On the metal side, the connector is an 11 mm nut; on the hose side, a 14 mm nut.  It was awkward for me to get all four pieces (the platform, the clip, the hose and the tube) into position so that I could start the thread, but I managed.

I am not sure but I am guessing that the rear brakes and the other E30 models and years work in a similar way.