Single Fin Box leash loop install: HOW DO YOU MAKE IT LOOK LIKE THIS?

So installing a leash loop in a single fin box: Drill a hole through the box into the deck, stick a length of cord through and knot it. Fine. Got it.


BUT what I cannot figure out: all of the boards I get done by the pros at production shops like Moonlight in San Fran, Glide Surf in Jersey, Deus in Bali -all have some kind of black or white resin plug surrounding the leash loop on the deck side. Is it some kind of plug insert? Or is it just a resin pour through the hole. I’ve attached photos below to show what I mean. 

If the hole is just drilled it looks tapered - is that a special kind of bit?

It looks so clean and nice - I would love to know how to do it.

It’s called a countersink.       The final step, after drilling the through hole.      Don’t overthink it.      

Many blessings.

Drill hole from deck side until you hit the bottom of the fin box.  

Mix pigmented resin and fill hole.

Let resin set

Drill hole through resin plug this time going through box.

Insert cord an tie off.

Go surfing.

I do it as part of fin box install. Route main hole for fin box. Test fit box. Mark where string should enter (all the way back in fin box slot, with room for knot. Remove box, drill hole at string location for resin plug to deck. If clever with a small Forster bit, can stop just at glass, but if drilled all the way thru, go slow for neatness, then tape over hole, twice in an x pattern just to be safe. Install box with usual mixture of pigmented thickened resin, extra glass if desired. When cured and board is rough sanded, drill thru plug and thru box using smaller bit. Counter sink for neatness. Install string and tie off before putting fin in box…

Plunge router.

Route box, set depth for full depth, route through deck.

Tape deck hole, install box.

After board is sanded, drill with a small bit from deck through box, (center of round resin hole), drill with a bigger bit 3/16".

Counter sink bit.

Leash plug

With the board fin side up, drill a 1/8" hole about 1/4" from the rear of the box through the box and deck.  Make sure this hole is straight.  Using a 1/2" forstner bit and the 1/8" hole as as pilot, drill from the deck until you hit the top of the finbox. Go about 1/16" into the bottom of the box.  Enlarge the 1/8" hole to 1/4".  Stick a piece of drinking straw into the hole until about 1/2" sticks out of the box and 1" up from the deck.  Put tape on the straw to make it fit tightly in the hole if needed.  Pour a pigmented, thickened resin mix from the deckside in the 1/2" hole around the straw, overfilling the hole slightly.  Pull out the straw as soon as the resin gels.  Sand the resin flush with the deck, mask the hole and lam a piece of cloth over it, hotcoat, sand, etc.  Loop and knot a piece of nylon cord and pull it through the hole from the box using string or wire.    

There are a couple of little details in phebus’ method which I like… he caps the whole deal on the deck with a piece of glass and he minimizes the risk of internal leakage where the resin fill meets the box by using the straw trick.  

I’ve had leak issues at both locations on an expensive custom board by a notable shaper that was glassed professionally at a notable glass shop.  The same glass shop rarely caps their fin box installs either and I’ve had leaks there as well.

I’d like to take credit for that install tip, but it’s one I found on here years ago. I’ve used it several times with great success. As others posted, I do dress the finished hole with a bevel to minimize the chance of cord breakage.