The odd shape at the end of the rubber line ensures that it can only go through in one orientation.
This means that the splitter where the vent bolt passes through is always pointed in the right direction.
On Ford's the left, drivers, side has an odd thread pitch and when you replace the brake lines you either need to reuse that nut or find a special adapter.
So, the odd shape passes through, and then the clip holds it tight to the cross member when you fit it in the groove that runs around the steel fitting.
Sorry, I don't have any pics and I can't walk right now.
Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.