I was wanting to add cup style QD for a sling. My larue has no attachment points on the forearm. It then occurs to me that they have little covers on the handguard that are screwed in with a hex screw. What kind of "style" is this? LaRue sells a specific QD for this but it's kinda steep. So, I was hoping to find something elsewhere. What style of mount do I need to make this happen? I'm used to M lock and key of, but I don't know what the LaRue is. Any tips?