Dimensional tables 8 and 9 allow for the use of cast iron (table 8) or steel (table 9). Since the modulus of elasticity of steel rings is higher than that of cast iron rings, the fluctuation in the surface pressure will become greater if the free gap is set as the reference for force. Therefore, forces are set using the surface pressure as the reference, in order to minimize the effect of the fluctuation.
The requirements of this document apply to rectangular rings for reciprocating internal combustion engines up to and including 90 mm diameter for cast iron rings and up to and including 100 mm diameter for steel. They may also be used for piston rings of compressors working under similar conditions.