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ISO3601 Overview

ISO3601 Overview – ISO3601-1, ISO3601-2, ISO3601-3, ISO3601-4 and ISO3601-5

ISO (the International Organization for Standardization) is a global federation of national regulations bodies. ISO3601 is a standard.

ISO3601 – Fluid Power Systems – O Rings

The Fluid Power Systems, power is remitted and directed via a fluid (gas or liquid) under stress inside a closed circle. To avert leakage or to seal diverse elements of a component from each other, sealing products are used. O Rings are an example of the sealing product.

ISO3601 Metric O Ring Sizes

Issued by International Organization of Standardization, the ISO3601 standard consists of 2 sets of O Rings, Class A, and Class B. Class A conforms to the American standard AS568B in its present structure. Class B permits the manufacture of O Rings in mechanically satisfactory and economical metric sizes, that suit metric grooves.

ISO3601 consists of the following 5 parts, under the general title ‘Fluid Power Systems – O Rings’:

  • Part 1 – Inside diameters, cross-sections, tolerances and designation codes
  • Part 2 – Housing dimensions for general applications
  • Part 3 – Quality acceptance criteria
  • Part 4 – Anti-extrusion rings (back-up rings)
  • Part 5 – Suitability of elastomeric materials for industrial applications

ISO3601 OverviewISO3601 OverviewISO3601 OverviewISO3601ISO3601 Overview


ISO3601-1 particularize the inside diameters, cross-sections, tolerances and designation codes for O Rings used in fluid power systems for widespread industrial and aerospace industry applications. The sizes (tolerances and dimensions) stated in ISO3601-1 are appropriate for any rubber material granted that adequate tooling is available.


ISO3601-2 particularize the housing (gland) dimensions for Class A O Rings for prevailing industrial applications complying with ISO3601-1. It also specifies housing dimensions for Class B O Rings used on preferred metric-dimensioned hardware, for example, piston rods or fluid power cylinder bores. These O Rings are intended to use in standard pneumatic and hydraulic installations with and without back-up rings (anti-extrusion rings). The sizes of the O Rings in ISO3601-2 size codes and tolerances conform to ISO3601-1.


ISO3601-3 specifies the quality approval standards of O Rings used in fluid systems, the sizes of which are regularized in ISO3601-1, ISO16031-, and ISO16031-2. This section of ISO3601 additionally specifies and categorizes surface blemishes on O Rings and defines uppermost acceptable restrictions for those blemishes. This part of ISO3601 also covers O Rings that are to be used in aerospace construction.


ISO3601-4 defines tolerances and dimensions for 5 categories of back-up (anti-extrusion) rings:

  • Type 1 – Spiral Type
  • Type 2 – Angle Cut Type
  • Type 3 – Solid Type
  • Type 4 – Angle Cut Concave Type
  • Type 5 – Solid Concave Type

These back-up (anti-extrusion) rings are intended for use with preferred O Ring sizes as defined in ISO3601-1 and the appropriate housing dimensions defined in ISO3601-2.


ISO3601-5 comprises the material description of a range of standard rubber (elastomeric) materials for O Rings used in standard industrial installations. It also defines the capacity of the materials to fulfil a number of demands involved with fluid power elements. Solely materials that are in global usage are defined, different elements are accessible and can be used.

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E & OE. M Barnwell Services endeavours to make sure that all the content is correct. Information has been gained from manufacturing partners.