If you look at the very first picture there is a hook with a screw right by the bottom. You just screw that into the bottom of the RIF by twisting it in. The second picture shows what it looks like screwed in. Guess I missed that part in the tutorial Sorry!
oh i understood that part. the part im refering to is the hand guard. hmmm.... ok im talking about step 12. it doesnt really make sense to me. originally the hand guard is flat. but then you manage to make some parts circular.