Introduction

At Hi-Tech Seals, we are fully compliant with ISO 3601-1 dimension and tolerance standards for all Class A standard series O-rings and Class B non-standard series O-rings. Our standard quality acceptance criteria for all O-rings is in accordance with ISO 3601-3 Grade N, while special orders for Grade S and Grade CS are available upon request. This classifies surface imperfections of O-rings and specifies maximum acceptable limits for these imperfections.

ISO3601-1 Dimensional Tolerances

ISO 3601-1 defines two classifications of O-rings, Class A and Class B. Class A have equivalent tolerances to those identified in AS568 and have tighter tolerances than Class B. They are suitable for industrial and aerospace applications or when the housing requires tighter tolerances. Class B O-rings are suitable for general purpose applications and have slightly wider tolerances than Class A O-rings.

ISO 3601-3 Quality Acceptance Criteria

ISO 3601-3 defines and classifies O-ring surface imperfections into one of three grades N, S, and CS.

• Grade N (general purpose) – Identifies the acceptance criteria for O-rings that are intended for general use applications
• Grade S (special) – Identifies the acceptance criteria for O-rings intended for applications that require a higher level of quality and or precision with respect to dimensional tolerances of surface imperfections
• Grade CS (critical service) – Identifies critical applications where a much higher level of quality and precision is required and the O-ring’s surface must be near perfect to perform in a satisfactory manner. For example, critical service aerospace or medial applications

The surface imperfections characterized by ISO 3601-3 include flash, excessive trimming, offset, non-fills, parting-line projection, back rind, flow marks, and indentations.