Finally got arround to field stripping my russian sks.had a few problems getting the release levers to move but everything came apart pretty good.rifle is in really good shape and everything seems to be tight and well fitting,however i have to wonder what the rod is that runs on the bottom of the barrel from the front site base back to the action,it has a treaded end on one end and a knob on the other with a hole in it looks like for turning it.but there is nothing for it to screw into.has me wondering whats this for?any one have an idea with out a picture?