What I don’t understand is I measured my receiver extension at 7 1/4”. When I received the lower the tube wasn’t screwed in far enough into the receiver to catch the buffer den-tent pin as soon as I took out the rear take down pin it all flew out like a slinky. I called customer service but I figured I could correct it my self instead of mailing it back I had spare castle nuts on hand ! Now I’m thinking that’s why it measures shorter than their spec