Have you ever had two things with rails that you wanted to put together. Maybe a shotgun with a top rail underneath your rifle or a pistol under an LMG. This mount lets you try all those crazy ideas. Best used for airsoft or paintball but might have some other applications.
Note: Buyer will need to provide 2x nut and bolt to clamp the mount together #8 1-1/4" works best. The piece connecting the two halves of the mount is temporary, cut it in half and discard, it is there to ensure the two pieces stay together in production/shipping.