Novoflex QPL 450 Double-Sided Arca-Style Rail - 17.7" Long 
The Novoflex QPL 450 Double-Sided Arca-Style Rail - 17.7" Long features an Arca-Swiss-style dovetail on either side, so you can attach it to a double-clamp system. For 3D applications, two cameras can be mounted to the long Q-Plate, one to each of the included 1/4"-20 screws, with horizontal positioning possible in order to adjust the interaxial distance between the cameras' optical centers.
Not only do the Q-series rails feature Arca-style profiles on either side, they also have 1/4"-20 & 3/8"-16 tripod mounting holes for direct attachment to a head or tripod. The rails serve as additional components for Novoflex's MultiMediaRig DSLR camera rigs (including Bluebird and uFly).