I have a new to me set of YHM forearms and cant seem to get them on. I can't get the delta ring low enough to get the bottom end in and secure. This is on the TOP or 3 rail portion. I can get the bottom bit in but not the top.

Any suggestions?

have someone help you or get the handguard tool

If i understand you right, I had the same problem installing handguards on one of my AR's. Try putting front end of handguard in cap first then tapping on back side of handguard with a very soft face mallet to make sure it is seated all the way in the handguard cap. This was all mine needed as the handguard was a much tighter fit then the original. If this works for you, after installed, then lightly tap Delta ring with the soft faced mallet to insure that Delta ring is fitted well aginst back side of handguard.

Ok guys, got it. thanks, nothing like a dead blow mallet to persuade parts.

Now just to get some rib covers, a handle and tac light and I'll be set...