Keyhole retainer

Vertical keyhole mounts work great because gravity keeps the mounting bolt in the narrow portion of the keyhole so the item doesn't fall, even when the bolts are loose.

Keyholes are less safe for horizontal mounts such as on the ceiling, since there is no natural tendency for the bolt to remain in the safe end of the slot. Worse, when tightening the bolt the movement has a tendency to walk the hung item along the keyhole slot.

This retaining clip locks the bolts into narrow end of the keyhole slots, making horizontal mounts safer. They are designed for a specific overhead power cord reel but could easily be modified for any keyhole mount.

The dimensions of the keyhole in this case are:

* 19.5mm for the large hole.
* 10.2mm slot width
* 35mm total slot length

It was a conscious design choice to make the hole in the retainer the same size as the slot, which is much wider than the bolt that I used. This allows for some slop in the distance between centers of the mount hol