These are all craps (dice) terms, and all are high-house percentage bets:
¶ to win the hard 6 bet, you must throw a hard 6, which is 3 on one die and 3 on the other die; it loses to: any seven thrown or any easy six (1-5; 5-1, 2-4, 4-2).
¶ to win a hard 4 bet, you must throw a hard 4 (2-2) before you throw any seven or an easy 4 (1-3; 3-1).
¶ to win a hard 8 bet, you must throw a hard 8 (4-4) before you throw any seven or an easy 8 (2-6; 6-2; 3-5; 5-3).
¶ to win a hard 10 bet, you must throw a hard 10 (5-5) before you throw any 7 or an easy 10 (4-6, 6-4).
These are all multi-roll bets; it is possible you will neither win nor lose on a roll, so the bets stay in place for the next roll, etc.
Here are some Hard 8 poker chips for sale at my auction. Chips not so rare, but this is my last set for sale: