70's board finbox

I have a board shaped in the mid 70’s, and the fin bolt broke off(old rusty) in the plate(nut) inside the box. It doesnt look like they made a way to remove the fin plate(nut) from the box in the original fins inlimited box, and now I cant put a fin in the box aaarrrhhhhggg! Any ideas on how to remove/replace the plate(nut) without damage to the box?

Go to a good industrial supply in your area and ask for an “easy-out”. To use the “easy out”, you drill the broken bolt, and tap the easy out in place. They are reverse thread, so as you insert the “easy out” it actually removes the broken bolt. Make sure that you get the proper size for your bolt and drill out the bolt with the proper size drill.

HI MILEAGE GAL HUH ?

Thank you Phil…I am very grateful for your help. Thank you