Most seal jobs come down to size, chemistry, and physical properties. Work the steps in order with the handbook tools you already have here.
Match the groove or the old ring to a dash number or metric size. Use the master chart for AS568 and ISO sizes, the groove charts for gland depth and width, or the calculators when you are designing from scratch.
Open the Master O-Ring Size ChartThe fluid decides which compound families survive, and temperature decides how hard that fluid works the seal. Search your media on the interactive chart, then confirm the compound can live at your min and max temperatures.
Search the Compatibility ChartConfirm temperature range, hardness, dynamic versus static duty, and any certification you need. Start with Shore A durometer for pressure and gap, then compare compound families and certifications.
Open Shore A HardnessShort, factual answers to the questions we field most.
Standard Nitrile (Buna-N) O-Rings work from -40°F to +250°F (-40°C to +121°C). For more heat, HNBR reaches +300°F and FKM (Viton®) reaches +400°F.
AS568 is the SAE Aerospace standard that defines inch O-Ring sizes. Each size has a dash number (such as -214) that encodes the cross-section and inside diameter.
EPDM is the standard choice for water, steam, and glycol brake fluid, rated -65°F to +300°F. Never use EPDM with petroleum oils, fuels, or greases.
FKM (Viton®) resists fuels, oils, and many chemicals up to +400°F. Avoid it with ketones, esters, amines, and hot water or steam.
Measure two dimensions: the inside diameter (ID) and the cross-section (CS, the cord thickness). When possible, measure the groove rather than a used ring, which can swell or take a set. We recommend Olypsys® over calipers, pi-tape, cones, and slide gauges for day-to-day identification. Full comparison: How to Measure an O-Ring. Deep dive on the app: how it works.
Most early failures are extrusion from too large a clearance gap, compression set from heat or over-squeeze, or installation damage from sharp edges and no lubrication.
Straight answers on compounds, sizes, and installation. No fluff.
Size charts, chemical compatibility, compound guides, groove design, and installation tips. Use the three-step finder above for a new seal, open O-Ring Basics for the fundamentals, or jump straight into the section that matches your problem.
Chloranthraquinone O-Ring guide for dye intermediate and specialty organic synthesis: chart ratings, why FKM is the preferred start, and which elastomers to avoid.
What IRHD means for O-Rings: ASTM D1415 / ISO 48-2 dead-load methods, Micro IRHD for thin cord and curved seals, why readings differ from Shore A (ASTM D2240), and how seal engineers use hardness.
Borneol O-Ring guide for fragrance and specialty organics service: chart ratings, why FKM is the preferred start, and which elastomers to avoid with this terpene alcohol.
Isobutyl chloride O-Ring guide for chlorinated solvent and alkyl halide service: chart ratings, why FKM is the preferred start, and which elastomers to avoid.
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