Details for M16 stock mod: Some minor cutting and filing is needed to insure the Airsoft AEG stock fits snugly into the Mossberg insert. I made the "notch" at the top about an 1/8th inch deeper. Some delicate filing is need at this point to make a nice fit. Cut off about 4 inches from the Mossberg collapsible-stock insert cylinder. attach a 10-32 T-nut onto the end of a 3" section of 3/4 dowel. Drill a 1\4 inch hole through the center of the dowel. Glue this inside the insert tube with polyurethane Gorilla Glue or equivalent. Countersink the opposite end of the dowel to ease the installation of the screw that came with the AEG stock. (the screw needs to be shortened to about 10 inches). The stock will rotate back and forth slightly few degrees from center after installing in the rifle so when you are satisfied the modified insert attaches correctly glue the modified Mossberg insert firmly into the stock.