Just a wild guess here -- Bob Stupak / Vegas World invented the "Crapless Craps" game.
That custom layout didn't have a traditional "Field Bet".
Maybe the "Field Bet" chips were designed to allow traditional Field bets at normal payouts??

I don't know if the chips were even used. I only tried Crapless Craps once, long ago.
Does Stratosphere still have a Crapless Craps table?