Hook & Pin Fin
This is the fin that comes on all Tower inflatable paddle boards today, and since about 2015. The fin box has a hole on the side toward the back of the board. A pin tethered to the fin base with a short rope is used to secure the fin to the board.
This is a proprietary iSUP fin box that has a built in hole for a fin screw inside the narrow fin box channel. The fins that accompany this have a screw permanently attached to the fin. This was used briefly on our Adventurer 2 10'4" model before summer 2015 and some older versions of the Xplorer 14' (sold spring and summer 2014). If you don't have those specific boards and your fin box looks like this, you should be buying the Hook & Pin Fin above most likely.
This is a universal long board fin box that you would typically see on hard surfboards and paddleboards, but they crafted a glue on fin box for inflatable paddle boards so you could use any long board fins on the market. There is not a screw hole in the fin box channel, as with standard longboard fin boxes your fin will come with a screw and a screw plate that you slide into the channel of the fin box and tighten. This was only used briefly on Xplorer 14' boards sold before Spring 2014. If you don't have that board, then your Tower iSUP will use one of the above fins and 99% of the time it will use the Hook & Pin Fin.