The most common surfboard fin systems (Futures, original FCS, Bahne/US Box) keep your fins in place with the use of a metal grub screw or screw/nut combination.
Overtime, you may find your screws have become stripped, rusted to uselessness, or lost all together.
Fortunately, finding a replacement is not too difficult. If you’re in a hurry, a trip to your local surf shop will do the trick. A good surf shop should have a handful of extra grub screws, slotted screws, and square nut plates. If you’re nice, they might just give you one – otherwise, they shouldn’t be too much more than 50 cents. If that doesn’t work, you can check your local hardware store too.
To keep your fins and fin hardware lasting longer try to wash them off with fresh water periodically, avoid over-tightening, and use a key/driver that fits snuggly and won’t strip the head.
Single Fin Pins, Screws, and Plates
Single fins are kept in place with a pin that sits in the slot of the fin box and are kept in place with a screw and square plate.
The size of longboard fin pin is 3/16” Diameter by 9/16” long. If you’re making your own fin or your pin fell out, you can affix a new one with a small amount of epoxy.
The size of a single fin screw is 10/32” x ¾”. The plates are about ½” x ½”. However, if you’ve lost the assembly altogether and are looking for a modified single fin system, you’ve got options there too.
Futures Fins Grub Screws & Allen Keys
Futures fins feature a single hex head grub screw that fastens the fin into the box.
Futures grub screws have a 10-24 thread and are 1/2” long. The hex heads take a 3/32 Allen key.
FCS Surfboard Fin Grub Screws & Allen Keys
The original FCS system use two grub screws, one for each tab. Each screw is 10-24 thread, 5/16” long. They can take a 3/32 Allen key as well.