It’s a rail mounting system. It came from the photography industry. The standard is from Really Right Stuff (RRS) with a 1.5” system, but now everyone is making them.
It starts with a rail attached to your gun that can manufactured by different people. Area419 is probably the common one. From there, you get arca plates and accessories to mount on a tripod arca head.
I’m sure a search of YouTube or Google would give you a better understanding.
Here are a couple pics of a rail by JP, made to fit their hand guards. Even though they fit the gas gun style guard, the rail itself is the same and attachments fit just like others.
Also, it makes it super quick and easy to slide attachments around the rail to various positions. Mainly used in PRS/NRL style comps. Plenty of info on YouTube about it...
Here are a couple pics of a rail by JP, made to fit their hand guards. Even though they fit the gas gun style guard, the rail itself is the same and attachments fit just like others.View attachment 7338322View attachment 7338323
It came with the screws, and I just put one in every hole. (That comment might fit in the MPT better, but you know what I mean). I just figured I’d use them all with a dab of blue loc tite, and I’d never have to worry about it, ever......