This Picatinny Rail is designed to be used as a riser on any flat-top Ar-15 or M-16
receiver. It is 5.04 inches long and provides space for a  BUIS (Back Up Iron Sight)
The rail has stainless steel thread inserts to prevent stripping of the bolt threads.
Picatinny Rail- 5
inch
(SM-1913-01)
$55