fin box

Slotted, rectangular plastic box set flush into the tail section of a surfboard to hold a fin. The fin box, as opposed to the fixed glass-on fin, allows the fin to be removed, adjusted, or exchanged, and also makes surfboard transportation easier. George Downing of Hawaii installed a handmade redwood-lined fin box into his big-wave balsa board in 1951, and Hobie Surfboards had an "exclusive remova...