this is a diamondhead 7" drop in carbine rail, brand new in blister pack. you have a pickatinny rail that runs full length on top. slots on the side and bottom for add on rail sections if desired. rail sections available on amazon or diamondhead directly. a very nice rail, i'm using one on an 80% build. asking $75. for shipping add $7. available for pick up also in the woburn area. contact via pm.