Standardized component groups for realizing basic operations of machinery and equipment. Includes general-purpose element parts commonly used in mechanical design such as bearings, gears, couplings, belts, chains, springs, screws, bolts and nuts. These components perform basic functions of power transmission, support, fastening, and cushioning in machinery, with many standard products complying with JIS and ISO standards. Distinguished from finished machinery and specialized parts, these are highly versatile component groups selected and integrated as machine elements from the design stage.