Home depot has a wide assortment of various sizes of conduit clamps, pipe clamps and hanger hooks. Here's some closeups of my installation. I used some old hanger hooks that I had laying around and a standard screw-type pipe clamp (I put a wing-screw on it for ease of removal) and mounted it to an existing screw and bolt.
I pop-riveted the hook in the overhead rail to avoid adding a bolt that might interfere with the door rollers. The galvanized channel on the wall above the door, that the cable snaps into, is "High-hat furring channel" by Gibraltar. It's hat-shaped, but you can squeeze it together by hand and the cable snaps in very nicely. I've used it to dress the cable all the way to my HPWC.
The lower hook (photo on right) uses a carriage bolt through an existing square hole in the rail.
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