SmallRig Tripod Mounting Kit W/15mm Rail Block 1798 is combined by two SmallRig Tripod mounting plates 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 a dovetail base plate. It clamps onto 15mm rails for accessory attachment, such as a follow focus, matte box, etc. The 40mm groove makes it possible to balance a front heavy camera on your tripod properly.