Fin/box Troubleshooting-- Won't Slide Past the Pin

[opelagos]

witched a fin into a new board and it won’t slide at back where the pin drops into the finbox; the rest of the base can sit fine in the finbox, but it just won’t slide back from the pin insertion point. Sanded it down a bit already, and didn’t see any glass drips in the box (though perhaps there's some where I can't see, like on the inside rim of the track where the plate slides). It seems site-specific, though I can't tell if it's an issue with the fin by the pin or something with the box.

Fwiw, fin fit fine into a different box; other fins I have on hand were slightly too fat for the box so I can't isolate that variable. Any thoughts on how to fix this? I guess I could just keep sanding the base of the fin by the pin but I'm wary in case that's not the issue, since it already works in other boards. Note: available tools are minimal (no power tools or chisels on hand). Thanks in advance!

[waikikikichan]

If the fin fits fine in other boxes, then don't sand down the fin. If the box is too tight side to side, get a flat head screw driver and drag it through the box front to back / back to front and gently scrape the sides. Check the fin fitting after a few passes.