I got sucked back into airsoft so expect more misc accessories over the months. This one is useful for things like canted sights, maybe a gopro mount, etc. It's meant to use a M4x35mm socket head cap screw and a nylon locknut, but a regular nut could be used too, and if you need an imperial size 8-32 should work as well. If it's tight on your rail either file it or scale up by a few percent. I also tried to make it as low profile as possible.
Added a split version 2015-12-30. The photographs show this version on my airsoft SR25. Note the tight clearance to the scope and how I wanted to use the stock flip-up sights as backup/close range sights.
Did mine in PETG and turned it flat on the bed, turned out pretty well!