the amateur World Eightball Pool Federation, as well as informal pub pool. The 7-foot size is also frequently used in North American amateur leagues, and are common coin-operated fixtures in bars and other venues. The playing surface for a 7-foot table is . Pockets Pockets, typically rimmed at the back with leather or plastic traditionally have drop pockets, which are small receptacles below each pocket to contain the balls. More modern tables may instead employ ball return pockets, a series of gutters inside the table, which deliver the balls into a collection compartment on one side of the table, in a similar manner to the ball return on a bowling alley. On a coin-operated table, the object balls are deposited inside an inaccessible window until the table is paid again, allowing the balls to be released into the compartment, while the cue ball is usually separated into its own ball return, often utilizing a different sized ball. A possible result of drop pockets is that if too many balls go into the same pocket, it would fill up the receptacle and prevent any more balls from going in that pocket, requiring that some be moved out of the pocket manually before shooting again. Regardless of table size, the WPA standard (sometimes informally called "American-style") table has wide, angular pockets that funnel notably inward, generally 1.75 to 2.25 times as wide at the opening as the diameter of the balls, wider at the side (middle) pockets than the corners. WEPF pool (sometimes informally called "British-style" or "Commonwealth-style") is played with balls, and this type of table has smaller, narrow pockets (the width is calculated as the ball diameter multiplied by 1.6, and is consistent at all six pockets), with rounded entrances and nearly parallel sides, like those on a snooker table. One tactical consequence of this design difference is that the jaws of the WPA-type pocket are often used exactly like a horizontal version of the backboard of a basketball goal, to rebound the ball into the pocket; this technique does not work on blackball tables, and even shots down the cushion into a corner pocket are more difficult. Bed For tournament competition under WPA world-standardized rules (and league play under derived rulesets), the bed of the pocket billiard table must be made of slate no less than thick. The flatness of the table must be divergent by no greater than