flatwounds, along with less squeaking, with a brightness generally between roundwounds and flatwounds. The polishing process removes almost half of the winding wire's mass; thus, to compensate for it, manufacturers use winding wire of a heavier gauge. Because of the extra manufacturing process involved, they are normally more expensive than roundwounds, but less than flatwounds. Core Types There are two types, or shapes, of core wire typically used in wound strings. Hexcore Hexcore strings are composed of hexagonal core wire and a tight (usually round) winding. Hexcore string design prevents the winding from slipping around the core – which can occur with round core strings. This may improve tuning stability, flexibility, and reduce string breakage, compared to round core strings. Round core Round core strings are composed of regular round core and a tight (usually round) winding. Round core is the traditional "vintage" way of manufacturing and results in a greater contact between the winding and the core of the string. Gauge Bowed instrument strings, such as for the violin or cello, are usually described by tension rather than gauge. Fretted instruments (guitar, banjo, etc.) strings are usually described by gauge—the diameter of the string. The tone of a string depends partly on weight, and, therefore, on its diameter—its gauge. Usually, string manufacturers that don't describe strings by tension list string diameter in thousandths of an inch (0.001 in = 0.0254 mm). The larger the diameter, the heavier the string. Heavier strings require more tension for the same pitch and are, as a consequence, harder to press down to the fingerboard. A fretted instrument that is restrung with different string gauges may require adjustment to the string height above the frets (the "action") to maintain playing ease or keep the strings from buzzing against the frets. The action height of fretless instruments is also adjusted to suit the string gauge or material, as well as the intended playing style. Guitar Steel strings for six-string guitar usually come in sets of matched strings. Sets are usually referenced either by the gauge of the first string (e.g., 9), or by pair of first and last (e.g., 9–42); measurements in thousands of an inch are the de facto standard, regardless of whether Imperial units are used in a country. Some manufacturers may have slightly different gauge sequences; the sample data below comes from D'Addario string charts for regular, round-wound, nickel-plated strings. Electric guitar