Five Oceans Marine Clamp-on Rail Mount VHF Antenna Base w/Adjustable Knob Handle for Boats, Plastic FO-1587 SUITABLE for all standard one (1) inch thread marine antennas TUBE CLAMP-ON Inner Diameter of 7/8" (22mm) MADE from ABS plastic to resist the marine environment KNOB HANDLE allows for redirecting antenna to multiples directions ATTACHES to 7/8" and 1" vertical, horizontal and angled rails. Comes with a hole for coax cable pass-through