The Rail Mount uses a Sony camera shooting at 120 fps in 720P but is technically not on the launch rail. It is located on a special mounting bracket at the top of the launch tower and the camera looks down on top of the rail.
This mount provides a unique perspective that can be amazing with the camera located so close to the rocket that it passes in between the fins of the rocket as it leaves the rail. As the rocket leaves the rail it passes within an inch or two of the Fixed Rail Mount. Of course it must be protected from the blast from the rocket motor so it is housed in an aluminium tube.
The construction of the mount is made from aluminium and welded together. It consists of a 4 foot long aluminium tube with plates welded to it. So the camera is actually located about 4 feet above the top of the launch rail. There is an angled tube that secures the plates together and deflects the motor blast as it passes. It is secured to the top of the launch tower with bolts.
The top of the mount is constructed from 8020 extruded aluminium with the protective aluminium housing welded to it. This top piece is removable and could be adjusted closer or further to the rocket if desired. This top piece is angled slightly so the camera has less tower in the field of view but this angle is not adjustable. The cables to control the camera are protected inside to the aluminium tube.