Help w single tab FCS dimensions

Any tips on sizing for single tab FCS fins? I’ve been making some canards w single tabs in mind for the first time, but in measuring out the tab size I’m having a little trouble.

Initially I was measuring out the tab size with a plug on its own (not installed) and they looked normal, felt good. but once the plugs were installed (by pro glass shop)it seemed like I had to keep removing material to get the fins to fit, and they don’t look right, and have gotten loose on occasion in the box. Part of that might be that I should make a little groove for the screw to go into, but I’m really just wondering if anyone can share some standards they’ve come across.

Thanks a lot,

Hi Tim
Here is a photo of a moulded plastic fin made by Shapers at Currumbin in Queensland.
The numbers are.
Tabs 20 1/2 mm
Tab depth 13 1/2 mm
Gap between tabs 33 mm
Orange FCS plug 23 mm therefore 2 1/2 mm bigger than tab so 1 1/4 mm of fin play.

I personally prefer the triplug fin box, slot for tab is 74 1/2 mm which gives 1/2 mm of play for the Shapers plastic fin (20 1/2 x 2 plus 33 = 74).

The tab screw always makes a mark on the fin tab.
I then drill into this mark using say a 10 mm drill bit making sure just to penetrate the tab slightly with the head part of the drill bit, a smaller drill bit is not recommended as you have less control and it can pull into the tab creating a deeper hole.

Marvin! Thank you man. This is why I posted here I knew someone had the details!
I wanted to be able to switch out these different fins, so it’s my first time doing them with plugs instead of just glasson.

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