Because of the ability of curves of constant width to roll between parallel lines, any [[cylinder]] with a curve of constant width as its cross-section can act as a [[Bearing (mechanical)#History|"roller"]], supporting a level plane and keeping it flat as it rolls along any level surface. However, the center of the roller moves up and down as it rolls, so this construction would not work for wheels in this shape attached to fixed axles.{{r|gardner|bs|rt}}
Several countries haveSome [[Coinagecoinage shapes|coins shaped]] asare non-circular curvesbodies of constant width;. examplesFor includeinstance the British [[British coin Twenty Pence|20p]] and [[British coin Fifty Pence|50p]] coins.Theirare heptagonalReuleaux shapeheptagons, with curved sides means thatand the Canadian [[currency detectorloonie]] inis ana Reuleaux 11-gon.{{r|chamberland}} These shapes allow automated coin machinemachines willto alwaysrecognize measurethese thecoins samefrom widththeir widths, noregardless matterof whichthe angleorientation itof takesthe itscoin measurementin fromthe machine.{{r|gardner|bs}} TheOn samethe other hand, testing the width is trueinadequate ofto determine the 11-sided[[Roundness (object)|roundness of an object]], because such tests cannot distinguish circles from other curves of constant width.{{r|gardner|bs}} Overlooking this fact may have played a role in the [[loonieSpace Shuttle Challenger disaster]], (Canadianas dollarthe coin)roundness of sections of the rocket in that launch was tested only by measuring widths, and off-round shapes may cause unusually high stresses that could have been one of the factors causing the disaster.{{r|chamberlandmoore}}
Because of the existence of non-circular curves of constant width, checking the [[Roundness (object)|roundness of an object]] requires more complex measurements than its width.{{r|gardner|bs}} Overlooking this fact may have played a role in the [[Space Shuttle Challenger disaster]], as the roundness of sections of the rocket in that launch was tested only by measuring different diameters, and off-round shapes may cause unusually high stresses that could have been one of the factors causing the disaster.{{r|moore}}
