SMALLRIG Railblock Rod Clamp for 15mm Rod DSLR Rig Rail System-60mm Spaced - 840 The railblock Rod Clamp can be mounted on any standard 15mm rods on DSLR Rig. Precision CNC machined from aluminum. Rails center-to-center distance : 60mm. And there are 4 types of Thread: 1/4", 3/8", M4 & M5 thread, which are very useful if you like to DIY DSLR Rig Ratchetting knobs, adjustable Levers, Metal M5 thread Knob Screw.