J4 corresponds to Junior medium and J5 corresponds to large

making it ideal for surf schools

the longer WK 540 is noticeably easy to drive but still stable enough for beginners

The zipper also works well when you get hot as you can open it to let in cooler air

Durable non-corrosive zippers

Choco Grip Sizes:20 J4 corresponds to Junior mediumChoco fins onshore wave fin. Gain control and grip in the waves with this fin that is designed for real conditions where waves are not always perfect. Works equally well in onshore and sideshore conditions. Made with CNC machine in G10. US box 20 Sail size: 3. 5 4. 5 sq m US box 21 Sail size: 4. 0 5. 0 sq m US box 22 Sail size: 4. 5 5. 5 sq m US box 23 Sail size: 5. 0 6. 0 sq m US box 24 Sail size: 5. 5 6. 5 sq m