SmallRig Tripod Mounting Kit W/15mm Rail Block 1798 is combined by two SmallRig Tripod mounting plate w/15mm rail block. Used for long length, front-heavy, camera packages. Attach it to the tripod plate with a 3/8”-16 screw and 1/4”-20 screw, then you can mount your dovetail base plate on it. It clamps onto 15mm rails for accessories attachment, such as follow focus, matte box, etc. The 40mm groove makes it possible to balance a front heavy camera on your tripod properly.