This replaces the rear site and is meant to be paired with the Rhino or Bison outer barrel.
Some filing may be required to fit them together depending on the precision of the printer used.
To mount the top rail use the screws from the rear site and one M3 screw used for the regular (AA official) picatinny rail.

Print the part on its side with supports to achieve the optimal strength for the bolt stop at the back of the rail