The M16A2 buttstock is about 5/8" of the inch more time then the sooner products. Because of the increased length it made use of a longer buttstock screw along with a spacer. The swivel is mounted closer into the buttplate. This buttstock is at this time utilised on the M16A4: https://raymondjrsqo.wikigdia.com/6683341/colt_m16a1_for_sale_fundamentals_explained