This has been the issue with several of the QD cup sling mounts I have seen in regards to improper installation. This causes an issue with your accessory not locking in correctly and having the ability to slide loose. If is in backwards like the photo below it causes a slight space between the edge of the shoe and the end of the KeyMod slot, which you can see in the next photo. There should be no gap or space between these pieces. This allows for the backer nut, which I am going to refer to as the shoe because that is exactly what it looks like, to slide in then forward as far as possible so that the shoe rests in the machined slot that it is made to fit into. The photo below shows the proper orientation for the backer nut in relation to the KeyMod slot. KeyMod is obviously a larger hole that is connected to a smaller, longer slot with a half circle on the muzzle end.

Please do not think that because I am doing a write up that KeyMod is complicated, because it is not, in fact it is probably simple enough that some folks are over thinking it.

so I thought I would throw together a write up with some photos. Alright folks, while bouncing around the forums I have seen a lot of people who either were against KeyMod, didn't understand it or loved it but were having issues attaching accessories.

Attaching keymod accessories