Remove the HPR and look up through the asa and you'll see where the SCM threads in. You'll be able to see the o-rings. Put some oil on the o-rings before you start. When you start screwing it in, use something to push the o-ring down while it's going in to keep it from getting pinched. I usually use a small screw driver. Just push the o-ring in a little bit, screw it in the SCM a little bit, push the o-ring in, etc.