I swear (based on nothing other than voodoo sensation) the Futures Key is a little thinner than FCS by just a shade. Like, you put a Futures key in FCS = Spearmint Rhino stripping. You put an FCS key in a Futures screw, she fits nice and tight.Side note, I once asked a dude for a "futures fin wrench" in the swamis parking lot, and he scoffed, told me they were the same as FCS (which he had). I stuck to my guns, opting to make him feel stupid rather than take it on the chin, and said "I'll take whatever gets my fin installed, but they're definitely not the same." However, I'm still not 100% confident in my stance, and I'm not going to take out digital calipers to measure.
Can someone edumacate me?
I think the threads on Futures boxes are different than the threads on the FCS boxes.
YMMV