A line, sometimes imaginary (especially in American pool), sometimes drawn on the cloth , that runs horizontally across the table from the second diamond (from the head rail ) on one long rail to the corresponding second diamond on the other long rail . In most pool games, the opening break shot must be performed with the center (base) of the cue ball behind the head string (i.e. between the head string and head rail ). The head string intersects the long string at the head spot , and delimits the kitchen (and, in European nine-ball , the outer boundary of the break box ). The head string 's position is always determined by the diamonds, in contrast to the similar but different baulk line , the position of which is determined by measurement from the bottom cushion (head cushion ).