yep, those are T-Nuts. perfect if you're ever going to have to remove your subs from enclosure down the line (for whatever) cause it doesnt matter too much if the screw holes strip out...use a nut and bolt application similar to this - make sure you pre-drill those holes to it fits nice and snug. those "prongs" get pushed into the wood - use light hits with a hammer to get them nice and tight. you might wanna use a drop of epoxy or super glue on the prongs to keep them from vibrating loose from the wood just in case.