This clamp fits a tank or board-type seat. Instant on/off with spring loaded adjustments. It attaches to your boat seat swivel or directly to the seat. Aluminum construction. Adjusts from 10"-18" in width.
I purchased two of these and was really impressed with their design and how they work. Seats stay put (even with my "large" father sitting in one!). My boat had 3/4" plywood bench seat with about 1" overhang on each side of the frame and these clamps fit perfect - real snug w/o any play whatsoever.