--- title: "ISO 3601-1 Metric O-Rings (ISO 3601) Specification" description: "ISO 3601-1 Metric O-Rings (ISO 3601): full dimensional table with tolerances. DIN, ISO and ASME equivalents listed side by side." url: https://engineeringhardware.com/guide/standard/iso-3601-1-metric-o-rings/ source: Engineering Hardware & Fasteners --- # ISO 3601-1 Metric O-Rings (ISO 3601) Specification Seals · ISO 3601-1 (fluid power — O-rings, inside diameters and cross-sections) Dimensional table, tolerance classes and the DIN / ISO / ASME parts that supersede or match this standard. ISO 3601-1 specifies the dimensions and tolerances for metric o-rings (iso 3601). The full dimensional table is reproduced below, followed by the DIN, ISO and ASME parts that match or supersede it. - **Standard:** ISO 3601-1 - **Product:** Metric O-Rings (ISO 3601) - **Governing standards:** ISO 3601-1 (fluid power — O-rings, inside diameters and cross-sections) Equivalence between national standards is dimensional, not always metallurgical. Check the property class separately when substituting. ![ISO 3601-1 Metric O-Rings (ISO 3601) Specification reference image](https://engineeringhardware.com/wp-content/uploads/2026/09/Metric-O-Rings.webp) Specification summary of ISO 3601-1 as applied to metric o-rings (iso 3601): the dimensions the standard fixes, the full size range supplied, and the related designations commonly cross-referenced. ## ISO 3601-1 — Scope The table below lists the dimensions catalogued for metric o-rings (iso 3601) under ISO 3601-1. The scope of ISO 3601-1 itself is not summarised here — where a figure matters, confirm it against the published document. ## Tolerance & Product Grades Product grade is a concept from dimensional fastener standards and does not apply to ISO 3601-1. Tolerances for this part are the limits shown against each dimension in the table. ## Dimensions Specified by ISO 3601-1 | Cross-section (mm) | Typical inside-diameter range (mm) | Common compounds | Notes | | --- | --- | --- | --- | | 1.0 | 1.0 – 20 | NBR, FKM, EPDM, silicone | miniature and pneumatic | | 1.5 | 2.0 – 40 | NBR, FKM, EPDM, silicone | small pneumatic and instrument | | 1.78 | 1.78 – 50 | NBR, FKM, EPDM | nearest metric equivalent to the 1/16 in section | | 2.0 | 3.0 – 100 | NBR, FKM, EPDM, silicone | general hydraulic and pneumatic | | 2.5 | 5.0 – 150 | NBR, FKM, EPDM | general hydraulic | | 3.0 | 6.0 – 200 | NBR, FKM, EPDM | general hydraulic | | 3.5 | 10 – 250 | NBR, FKM | hydraulic | | 4.0 | 12 – 300 | NBR, FKM | hydraulic and larger flanges | | 5.0 | 20 – 400 | NBR, FKM | large flanges and covers | | 5.33 | 20 – 400 | NBR, FKM | nearest metric equivalent to the 3/16 in section | | 6.0 | 25 – 500 | NBR, FKM | large covers and housings | ## Equivalent Standards Where direct equivalents exist (ISO ↔ DIN, ISO ↔ ASME), they are listed on the parent Metric O-Rings (ISO 3601) page. Always confirm against the dimensions on this page, since some "equivalent" standards differ in tolerances and head geometry. ## Companion Standards A complete specification for metric o-rings (iso 3601) normally cites several documents: one for the geometry, one for the material or mechanical properties, and one for the finish. ISO 3601-1 is one of them, not all of them. Custom manufacturing · Made to drawing ## Need a seal to this standard in a non-standard size? Parts built to ISO 3601 1 are already in the catalog, so a special is usually a variation on existing tooling rather than a new design — which is what keeps the cost down. Minimum order from 2,000 pieces; samples within 7 days of drawing approval. [Custom seal manufacturing](https://engineeringhardware.com/custom/seals/)[Send a drawing](https://engineeringhardware.com/custom/seals/#rfq) ## Technical Drawing Dimensioned line drawing of 1.0 Metric O-Rings (ISO 3601) to ISO 3601-1 (fluid power — O-rings, inside diameters and cross-sections). Side view and top view, drawn to the dimensions in the table below and redrawn for any size selected. - **Typical inside-diameter range (mm):** 1.0 – 20 - **Common compounds:** NBR, FKM, EPDM, silicone - **Notes:** miniature and pneumatic ## Dimensions & Specifications (ISO 3601-1 (fluid power — O-rings, inside diameters and cross-sections)) | Cross-section (mm) | Typical inside-diameter range (mm) | Common compounds | Notes | | --- | --- | --- | --- | | 1.0 | 1.0 – 20 | NBR, FKM, EPDM, silicone | miniature and pneumatic | | 1.5 | 2.0 – 40 | NBR, FKM, EPDM, silicone | small pneumatic and instrument | | 1.78 | 1.78 – 50 | NBR, FKM, EPDM | nearest metric equivalent to the 1/16 in section | | 2.0 | 3.0 – 100 | NBR, FKM, EPDM, silicone | general hydraulic and pneumatic | | 2.5 | 5.0 – 150 | NBR, FKM, EPDM | general hydraulic | | 3.0 | 6.0 – 200 | NBR, FKM, EPDM | general hydraulic | | 3.5 | 10 – 250 | NBR, FKM | hydraulic | | 4.0 | 12 – 300 | NBR, FKM | hydraulic and larger flanges | | 5.0 | 20 – 400 | NBR, FKM | large flanges and covers | | 5.33 | 20 – 400 | NBR, FKM | nearest metric equivalent to the 3/16 in section | | 6.0 | 25 – 500 | NBR, FKM | large covers and housings | Product catalog ## 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Applications & Industries Where Metric O-Rings are used, and what decides the specification in each case. Stocked from 1.0 to 6.0 (inside diameter). ### Industries that specify Metric O-Rings - **Hydraulics:** Port, cover and piston seals. - **Pneumatics:** Cylinder and valve seals. - **Food and beverage:** EPDM and silicone compounds. - **Chemical plant:** FKM for aggressive media. - **Hydraulics & pneumatics:** Static and dynamic sealing in cylinders and valve bodies. - **Process & food equipment:** Sealing at joints that are cleaned and inspected. ### Typical applications - specifying inside diameter, cross-section and compound together - matching the compound to the fluid and the temperature - checking the groove dimensions give the right squeeze - using a back-up ring at high pressure - sealing a joint against fluid or air pressure - excluding dust and moisture from a housing ### Service conditions to specify against - **Sealed joints:** Used where the fixing has to keep water or air out as well as hold — the elastomer, not the fastener, decides service life. ### Where to use something else - Do not substitute an NBR ring for an FKM one because the dimensions match; the size fits and the compound fails, which looks like a leak with no cause. [Full application guide: where Metric O-Rings are used, how to specify them, and the cases they are wrong for](https://engineeringhardware.com/applications/metric-o-rings/) Inside the plant ## Manufactured in our own plant This part is cold-formed, threaded, heat-treated and finished in-house. The stages below are where its class and finish are actually decided. 1. ![Wire rod feeding into a cold heading machine](https://engineeringhardware.com/wp-content/uploads/2026/08/09-wire-rod-feed-cold-heading-machine.webp) 01 **Cold heading** Wire rod is drawn to size and cold-formed into blanks. Forming rather than cutting keeps the grain flow continuous around the head, which is where a bolt is most likely to fail. Head dimensions and under-head radius checked at set-up and per shift. 2. ![Thread rolling machine producing bolt threads](https://engineeringhardware.com/wp-content/uploads/2026/08/03-thread-rolling-machine-bolt-production.webp) 02 **Thread rolling** Threads are rolled between hardened dies rather than cut. Rolled threads are stronger in fatigue than cut threads and hold pitch and flank angle far more consistently across a batch. Go / no-go ring gauges to ISO 965 tolerance class 6g. 3. ![Baskets of bolts staged for heat treatment](https://engineeringhardware.com/wp-content/uploads/2026/08/05-heat-treatment-baskets-black-bolts.webp) 03 **Heat treatment** Quench-and-temper brings carbon and alloy steel to the property class ordered — 8.8, 10.9 or 12.9 — with the furnace charge tracked so a finished lot can be traced back to it. Core hardness and tensile tested per lot to ISO 898-1. 4. ![Zinc plated bolts in a treatment basket](https://engineeringhardware.com/wp-content/uploads/2026/08/23-zinc-plated-bolts-treatment-basket.webp) 04 **Surface treatment** Zinc, zinc-nickel, hot-dip galvanizing, black oxide, phosphate and Dacromet, selected against the service environment rather than against the price list. Coating thickness and neutral salt spray hours to ISO 9227. ## Frequently Asked Questions ### Which edition of ISO 3601-1 does this table follow? The table reproduces the dimensions we supply metric o-rings (iso 3601) to. We do not publish an edition year against it, so where the edition is contractually significant, cite the edition you require on the enquiry and we will confirm it against the table before quoting. ### Can I substitute ISO 3601-1 for the corresponding DIN standard on a drawing? On modern drawings the ISO standard is the master reference; the older DIN equivalent is a cross-reference. For most dimensional purposes the parts are interchangeable, but check tolerance grades and the head height — these are the most common points of divergence. ### How do I request a quotation? Use the technical drawing on this page to pick the exact configuration, then submit it with the quote form. We respond within one business day. ## Related Pages [View the full Metric O-Rings (ISO 3601) page](https://engineeringhardware.com/fastener/metric-o-rings/)