Internal combustion engines -- Piston rings -- Part 4: General specifications
Это стандарт пересмотрен ISO 6621-4:2015
ISO 6621-4:2003 specifies the general characteristics of piston rings for both reciprocating internal combustion engines and compressors (the individual dimensional criteria for these rings are given in the relevant International Standards). It also provides a system for ring coding, designation and marking. It is applicable to all such rings of a diameter greater than or equal to 200 mm.