ConnexSUP Master Plug and Slotted (FCS Fin plug style) insert. This includes both the base plug and the insert plug. The slotted insert plug is typically used for mounting GoPro cameras to a board using a GoPro mount (mount not included).
Probox fin boxes are designed to accept different inserts that change the cant of the fin (the angle in relation to the bottom of the board and the side of the fin) so that you can tune in your ride. Inserts are available in 0, 4, 6, and 8 degree as well as solid inserts to plug boxes not being used.