Curious about all the different types of fins?

Every day we receive questions like "How do I tell which fin my SUP / kayak has? Which fin types are there anyway and which adapters are offered when buying a JayKay e-fin". Since this topic is not quite so quickly and easily explained, we have written this post for you.


As nice as it is to be able to choose a SUP from an ever increasing variety and number of suppliers. The difficulty of then having to select a suitable adapter for the e-fin increases as a result. Add to this the fact that there are no uniform standards for fin mounts. Each manufacturer can design and manufacture their own fin shape and mount. Unfortunately, it is not always the case that a manufacturer sticks to just ONE fin mount. Sometimes it is even the case that there are small variations in the same fin mount depending on the year of manufacture.

The difficulty for us here was to create a suitable adapter for each recording type with its deviations and also to be able to declare this for the customer in an understandable way.


The positive, however, right up front: There are 3 fin mounts, which are installed by most manufacturers. For these recordings you get suitable adapters in our store:



A characteristic feature of the Slide-In fin mount is the safety pin hanging on a cord. This is always pushed into the existing slot on the side after the fin is mounted to secure it.

Slide-In Fin / Adapter

This fin mount is present in about 75% of all SUPs. Among other manufacturers such as Aqua Marina, Ocean Fit, DURAERO, Aukai, Naish, Aztron and many "no name" - brands.

Important here is to observe the minimum dimensions of the fin box despite everything: Length 1800mm x width 18mm.

Decathlon's ITIWIT SUP line, for example, is increasingly offering SUPs with shortened slide-in mounts. On the following photos you can see the difference:




Besides the slide-in mounts, the US box mount is also one of the most common fin mounts, especially for high-end SUPs. You can find them among others at manufacturers like Starboard (standard series), Naish, JP Australia, Cruis Air, Indiana SUP, Aztron and Bluefiin.


The US-Box fins are inserted into a rail from the underside with a slot stone and then screwed from below with an external screw.

The minimum dimensions of the fin box are: length 208mm x width 9mm.

There are also exceptions to this fin mount with some manufacturers:



The Deluxe series of Starboard has a slightly downward offset groove stone, which requires an adapted US box adapter from us. This should be communicated during the ordering process simply via the comment function in the shopping cart or via eMail ( to our service team.



Aztron still has a US box mount for the models from 2020 onwards, but the screw is on the opposite side. This also requires a specially adapted adapter, which should be communicated to the JayKay team during the ordering process.


US Softbox / Split fin box

The US softbox is a split fin box mount. There is a JayKay adapter for this, but we do not recommend it due to slight radio interruptions.  



The Smartlock mount is still relatively new but is becoming more and more established. Brands like Bluefin (Cruise model), iRocker SUP and JOBE use them.


Instead of using a locking pin or screw as in previous systems, this system relies on a locking hook. The fin is inserted into the box and then fixed with a hook, which is located on the fin box. This has the advantage that the fin can be mounted quickly and without tools.

The minimum dimensions of the fin box are: Length 165mm x width 9mm.


The following fin mounts are very common, especially for surfboards. Since we reach our mechanical limits here, we can unfortunately not yet offer JayKay adapters:



The manufacturer FCS (abbreviation for Fin Control System) is the world's leading manufacturer of fins for surfboards. FCS developed and patented the FCS fin system in 1995, which over the years gained a huge market share in the surf sector.

The advantage of the FCS II fin system is that it works completely without screws or locking pin. The system consists of two round fin plugs into which the two "nose pieces" of a fin are inserted and click by pressure.


FCS II (Connect)

In this system, the fin box is built analogously to a US box, but this system is mainly used on hardboards, where the fin mount is recessed directly into the board. This receptacle also has the advantage that the fin only needs to be inserted and pressed down.


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