This design holds an airline to the aluminium frame of our test lab. ~RELAGATED TO WIP AS NEWER, BETTER VERSION AVAILABLE~ Size Ø16 & Ø12: http://www.thingiverse.com/thing:642899 The Test Lab is made of a standard Aluminium Section Beams - no idea what they are called : PM me or add a comment below. I've added a hole and boss either side of the hooks after version 1 so that two can be pressed together once in posiiton and that will stop them rotating out of the slots. I've updated side features to allow the retainer to clip in using same features as the anti rotate protrusions. Added a couple more updated files, it should be possible to assemble the retainer / lock into the hook before placing the hook into the aluminium channel and twisting 90° to lock into position. Still not entirely happy. I'll print both of these parts tomorrow and critique.