Materials
You'll need a double-six domino set. Use every piece except the double-zero. The 22 tiles are divided into seven suits and ranked the same as in Texas 42. The suits are: zeros, 1s, 2s, 3s, 4s, 5s and 6s. In each suit the double tile is the strongest; for example, among the twos, 2-2 is stronger than 2-6, the next strongest tile in that suit.
Each tile has two numbers, so potentially a tile can belong to one of two suits depending on which trump is called at the beginning of the hand.
Dealing
Each player takes seven tiles. The extra tile remains face down on the table.
Bidding
Players make bids for how many tricks they may win. Bidding goes clockwise around the table, and each player is allowed to bid once. Players may choose on the fly who will begin the bidding on the first hand; first bids then move one chair to the left for subsequent hands.
Players can bid three ways: they may pass, choose a number between four and seven, or go "all in" and call 21. Bidding 21 is called "shooting the moon" because it means the player is betting they'll win all seven tricks. Shooting the moon is the only way to outbid a 7, and should the auction winner win all the tricks, they score 21 points rather than only seven. If players don't pass or call 21, each consecutive player must bid higher than the last player's bid. Bidding ends when a player calls 21 or all players have bid. Whoever bid highest swaps out a tile for the extra on the table and must name trump.
Trump may be any number from 0 to 6. If the trump is zero, double-zero is the only trump possible in that hand. The auction winner may also call doubles as trump. In this event, all double tiles ̵2; 4-4, 2-2 and 1-1, for example ̵2; are their own suit with the strongest being 6-6. Or, no trump may be called. This method is called "follow me," and it means simply that doubles are the strongest in each suit.
Playing
The auction winner leads with any tile toward the first trick. If the tile played is a trump, other players must play trumps if they can. If they can't, any tile may be played. If no trump is played, the high side determines that hand's suit. Again, players play to that suit if they can. If they can't, any tile may be played.
If a trump is played, the strongest trump wins the trick. If no trump is played, the highest tile of the given suit wins. The trick winner takes the three tiles, stacks them on the table face down, and begins the next trick. This mode of play continues until all tiles have been played.
Scoring
The auction winner must take at least as many tricks as the bid to earn that amount of points. No extra points are rewarded for scoring more than the bid.
If the bidder fails to claim as many tricks as was bid, the bidder scores an equal amount of negative points.
Each trick won is worth one point. For example, if a player calls six tricks and wins them, he wins six points. Another player wins the remaining point.