The ball sets typically range from 2 inches (50.8 mm) up to 2 3⁄16 inches (56 mm), often with a slightly smaller cue ball, e.g. 1 7⁄8 inches (47.6 mm) for a 2-inch set. The most common sized sets on the market are 2 inches and 21⁄8 inches (54 mm). Along with the single white cue ball, plain unnumbered red (or sometimes blue[5]) and yellow colour balls, seven of each colour, are used in lieu of the numbered solids and stripes common to international eight-ball and other pool games. Many (especially North American) suppliers refer to the yellows-and-reds sets as "casino" balls, whether UK- or US-sized, because they were formerly used in US casino-hosted, televised, modified-rules eight-ball tournaments popular in the 1970s; the coloured rather than numbered sets were selected for their distinguishability on TV. The black ball, however, still typically bears a number "8" (a holdover from kelly pool), though numberless variants are not unknown.
