CowboyStudio Professional Mount Rail Block Rod Clamp Rig for 15mm Rod DSLR Rig Rail System Follow Focus One (1) Rod Clamp DSLR rig connector with 1/4" thread Fit all 15mm rod system. There's a spacer between the knob and the clamp, this can protect the clamp and the knot from scratch. With precise design, small size and durable.