Specifies the essential dimensional features of R-, B- and M-rectangular piston ring types. Dimensional tables 8 and 9 offer the choice of two radial wall thicknesses: "regular" (table 8) or "D/22" (table 9). The requirements of this part apply to rectangular rings for reciprocating internal combustion piston engines, up to and including 200 mm diameter. May be used for piston rings for compressors working under similar conditions. Several figures illustrate shapes and reference quantities of concern.