ISO 16589 specifies seals utilizing sealing elements manufactured from suitably formulated compounds based on thermoplastic materials, such as polytetrafluoroethylene (PTFE). They are considered suitable for use under low pressure conditions. This part of ISO 16589 defines and classifies typical surface imperfections that could impair the function of the seals, and is intended as a convenience for purchasers and manufacturers in their discussions concerning the importance of these imperfections in different applications. NOTE ISO 16589 is complementary to ISO 6194, which covers seals incorporating elastomeric sealing elements.