I'm cornfused brother.I think the buffer tube goes on the same sa on a 15.back off the castle nut,screw in buffer tube till it touches buffer retaining pin and back off so pin moves up and down without binding.Then rotate back plate to hold rear take down pin spring in said hole with detent in front of spring.This also has a notch that aligns buffer tube so the stock adj. holes are @ 6:00 position.Then tighten nut.If nut doesn't move far enough forward to tighten aganist plate,then the threads are scarred [ easy to do since it aluminum].If you have something thin enough you might be able to chase the thread.If it is really smashed you might need a new tube.This all relative to collapsable stock setup.The retaining plate I have is from a 15,if it's the same for a .308 you can have it.I would think if you had to you could duct tape castle nut,put a rag on a pair of channel locks and snug it up. <dontknow>