You'll need to buy a "spanner wrench. Older wrenches have one or two lugs, the new style have three.
You'll need to figure out which you have.
Here's the new style:
http://www.bushmaster.com/shopping/gunsmith/223-telewrench2.asp
Here's a AR-15 diagram for the actual stock assembly:
http://www.e-gunparts.com/productsc...660zAR15 SPORTER - SLIDING BUTTSTOCK ASSEMBLY
Here's the diagram for the lower receiver assembly.
http://www.e-gunparts.com/productschem.asp?chrMasterModel=0660zCAR15 - LOWER RECEIVER ASSEMBLY
Remove the buffer and the buffer spring.
Remove the stock assembly by pulling down on the rear edge of the latch part number 10, and sliding the entire stock off the tube.
Use the wrench to unscrew the round nut on the very rear of the lower. In the diagram, this is part number 3.
When unscrewing the nut, BE CAREFUL to catch the take down plunger and spring parts number 9 and 10, and the take down pin part number 15.
The take down spring and plunger are held on by the plate, and these retain the take down pin.
DO NOT unscrew the buffer tube as this will release the buffer retainer pin and spring parts 5 and 6.
With the nut off you can install the sling adapter.
I assume this adapter replaces the frame plate, part 2.
Fit the adapter over the buffer tube and slide it forward, making sure you have it right way around.
It should have a large dimple that fits into the hole in the lowers rear face.
Slide the stock nut over the buffer tube with the notches facing FORWARD.
Install the take down pin and the take down spring and plunger, then press the adapter forward and screw the nut on, making SURE the take down pin is in place, AND that the spring goes into the hole in the lower as the nut is snugged up.
With the nut snug, check the take down pin to insure it's in position and works properly and that the take down spring is in place.
Make sure the buffer tube is properly aligned and hasn't turned slightly.
Hold the buffer in place and use the spanner to tighten the nut tightly.
If you want, you can stake the nut in place by using a punch to move some metal from the adapter into the notches on the nut.
Re-install the stock.
