The Net & Gaff Holder for the rail system has a tough base mount made from UHMW with a nylon thumb screw for locking it in position on the rail. The top hoop is constructed from Starboard the internal diameter of the hoop is 1.5". This holder is designed specifically for our rail system but we also have net and gaff holders that direct mount to the vessel they are part MMP-1013 and they do not mount to the rail.