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.
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Surfboard Fin Screw Sizes
- Futures grub screw: 10-32 x 1/2″
- FCS grub screw: 10-24 x 5/16″
- Bahne/FU/Standard Longboard/SUP Center Fin:
- Screw: 10-32 x 3/4″
- Plate: 1/2″ x 1/2″ x .15″
Single Fin Screw Size
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 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.
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.
You can also find thumb screws for your single fins that make changing them out and adjusting them on the fly possible.
Futures Fins Grub Screw & Allen Keys Size
Futures fins feature a single hex head grub screw that fastens the fin into the box.
Futures grub screws have a 10-32 thread and are 1/2” long. The hex heads take a 3/32 Allen key.
FCS Surfboard Fin Grub Screw & Allen Key Sizes
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.
Fixing a Stuck or Stripped Fin Screw
If you surf for long enough, the chances are good that you’re going to run into some issues when installing or removing your fin screws.
The difference between a potentially ruined session and an enjoyable surf is whether or not you’ve got some replacement hardware.
It’s always good to be prepared. That’s why you should stock up on some fin screws and handy fin tools before you run into problems.
Rusted screws, stripped heads, stripped fin box threads. It has happened to many surfer before you and it can happen to you.
These are the reasons to keep back-up fin screws on hand in first place. Rusted screws, seized screws, stripped screws, etc. – All of these are things that most surfers will experience at some point in their surfing experience.
If you’ve got a busted fin screw, chances are you’ll need a replacement – hence the recommendations above.
However, in some situations, you’ll need more than just a replacement screw. You’ll need a way to get the broken screw out or fix the stripped threads.
It’s not always easy, but there are a few methods you can try when dealing with stuck/rusted fin screws or stripped fin box threads.
To remove a stuck fin screw:
- Soak it in penetrating oil or WD-40.
- Try to back it out.
- If it doesn’t work, glue a sacrificial fin key or allen wrench to the screw, allow it to dry, and remove it.
If the threads in your fin box are stripped, you can either:
- Fill the screw hole with a quick set epoxy (plug the bottom first).
- Allow the epoxy to set.
- Use a #21 drill bit or bit smaller than your grub screw to drill through the center of the epoxy.
- Use a new grub screw and tighten it through the hole to retap the threads.
- Use a slightly larger size tap and grub screw and retap the stripped threads.
Preventing Problems with your Fin Screws
You can prevent all of the above with a little preventative maintenance.
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.
- Be sure to rinse the salt water off your fin screws and fin boxes after a surf.
- Avoid over-tightening your screws.
- If you feel a bad (loose) seat between the fin key and the fin screw, don’t try to tighten or untighten it. Instead, find an allen key with a better fit, remove the screw, and replace it with a new one.