2 1/4 inch (57mm) Plastic 9 Ball Rack. Nine ball diamond for racking the balls for 9 ball American Pool.
For balls to fit these triangles please see below:-
Nine-Ball is played with nine object balls numbered one through nine and a cue ball. On each shot, the first ball the cue ball contacts must be the lowest numbered ball on the table, but the balls need not be pocketed in order.
If a player pockets any ball on a legal shot, he remains at the table for another shot, and continues until missing, committing a foul, or winning the game by pocketing the 9-ball.
After a miss, the incoming player must shoot from the position left by the previous player, but after any foul the incoming player may start with the cue ball anywhere on the table.
Players are not required to call any shot. A match ends when one of the players has won the required number of games.