If you took the steel bar out of a leash plug can you fit a FCS tab into it? I don’t have any FCS fins around so I can’t try it myself. If you can maybe you should buy a drill tap and make your own FCS pugs?
Dean,
Many reasons it wouldn't be a good idea. I don't think the material leash cups are made from is as strong and they are fairly shallow in depth and lack an outer surface configuration that would provide for a strong installation. My 2 cents.
regards,
Dave D