The Baseplate provides 4 1/4"-20 threaded holes and 3 3/8"-16 threaded holes for standard tripods. It also comes with more three 1/4" mounting holes on the other end, you can attach another 15mm railblock for better stability.The 15mm Railblock features standard 15mm rod holes, 60mm apart center to center. Compatible with 15mm rod or lever. It provides 5 1/4"-20 thread holes and 1 M5 thread hole. The knob with adjustable design.