Flat washers, also referred to as Type A plain washers, are thin, flat, and circular general-purpose washers with a centrally located hole. Standardized flat washers may be designed by the use of imperial or metric dimensions. Standard imperial washers include SAE washers, for use with fine threaded nuts and bolts, and USS flat washers, for use with coarse threaded bolts and nuts. Standard metric washers are available in several gages as defined by JIS standards.