The Rifle length PRI #38 SPR top rail for Gen III round forearms is a full Picatinny rail that connects the receiver to the forearm. The forearms 8.5" rail with lugs is required to install top rail.  To help with alignment of the top rail to the full length top rail loosen screws holding 8.5" rail to allow it to slide back and forth. Install full length top rail and install the 2 1/4 x 20 flat head screws and then tighten everything down.  The #38 rail has 15 pressed lugs (#10-32 thread) installed down the rail for attachment points, unique clamp bar with square screws to lay in the receiver channels, locks down with 3 (#8-32) locking nuts.  Rail is notched out over the BN area for PRI gen III forearms.