CAMVATE 15mm Rod Clamp Railblock for DSLR 15mm Rail Rig Rod Support System The 15mm Railblock is made of solid aluminum. Features standard 15mm rod holes and 60mm center to center distance. There are both five 1/4"-20 tapped mounting holes on top and bottom add to its understated versatility. The 15mm Railblock is also our accessory for Top Handle and Top Plate Handle Grip for BMCC.