Nitrile O-Rings
NBR / Buna-N
Wayne Rubber manufactures custom nitrile (NBR / Buna-N) o-rings for hydraulic systems, fuel handling equipment, automotive applications, and industrial machinery. Available in all AS568, ISO 3601, and metric standard sizes, as well as fully custom dimensions — with in-house compound formulation across the full NBR durometer range.
Why Nitrile for O-Rings?
Nitrile rubber — also called NBR or Buna-N — is the most widely used elastomer for o-rings globally, and for good reason. It offers the best combination of oil and fuel resistance, mechanical strength, and cost-effectiveness available in any general-purpose sealing compound. For any application involving petroleum-based oils, hydraulic fluids, fuels, or lubricants, NBR is almost always the starting point for material selection.
The key performance variable in NBR is its acrylonitrile (ACN) content, which typically ranges from 18% to 50%. Higher ACN content increases resistance to oil and fuel but reduces low-temperature flexibility and compression set performance. Standard general-purpose NBR compounds run around 32–34% ACN — a balance point that suits the majority of hydraulic and fuel system applications.
NBR’s main limitations are its poor resistance to ozone, UV, and outdoor weathering — for outdoor or weather-exposed seals, EPDM is the correct choice. NBR also degrades quickly when exposed to polar solvents, ketones, or strong acids. For high-temperature oil service above 250°F or aggressive chemical environments, HNBR or FKM should be evaluated.
Wayne Rubber compounds NBR in-house, allowing us to tailor ACN content, durometer, and additive packages to your specific operating environment. Use our Chemical Resistance Guide to verify NBR compatibility with your specific fluids.
Nitrile O-Ring Material Specifications
Standard NBR compound properties for o-ring applications. Wayne Rubber can formulate custom NBR compounds for specialty service requirements including low-temperature flexibility, FDA compliance, or elevated oil resistance grades.
| Property | Standard Value / Range |
|---|---|
| Temperature Range | −40°F to +250°F (−40°C to +121°C) Low-temp grades to −65°F; high-temp grades to +275°F |
| Hardness (Durometer) | 40 to 90 Shore A Standard grade: 70 Shore A (NBR-70) |
| Acrylonitrile (ACN) Content | 18% – 50% Standard: ~33% ACN. Higher ACN = better oil resistance, reduced low-temp flexibility |
| Tensile Strength | 1,000 – 3,000 psi (typical) |
| Elongation at Break | 100% – 600% (compound-dependent) |
| Compression Set | Good (standard) — Excellent (low-compression-set grades) |
| Color | Black (standard) — custom colors available |
| ASTM Designation | ASTM D-2000 Class BF, BG, BK (grade-dependent) |
| Petroleum Oil Resistance | Excellent |
| Fuel Resistance | Excellent (aliphatic hydrocarbons); Good (aromatic fuels) |
| Water Resistance | Good |
| Ozone / UV Resistance | Poor — not recommended for outdoor exposure |
| FDA Compliance | Available — FDA 21 CFR-compliant NBR grades upon request |
Size Search & Gland Design Tools
Wayne Rubber’s technical tools let you identify the right o-ring size and design the gland to match — before you contact us for a quote. Both tools are free and require no login.
Search 1,400+ standard nitrile o-ring sizes across AS568, ISO 3601, Metric, and JIS B2401. Look up by dash number, ID, or cross section. Full tolerances in inches and mm.
Calculate gland depth, groove width, squeeze percentage, and gland fill for piston, rod, and face seal configurations — covering all five AS568 cross-section series.
NBR O-Ring Grades & Formulation Options
Not all nitrile o-rings are the same. Wayne Rubber’s in-house compounding allows us to formulate NBR to your specific performance requirements rather than supplying a single off-the-shelf grade.
The most common o-ring compound worldwide. 70 Shore A, ~33% ACN content. Suitable for hydraulic fluid, petroleum oil, water, and general industrial service from −40°F to +250°F.
40–50% acrylonitrile content for maximum resistance to aromatic fuels, high-aniline-point oils, and aggressive petroleum solvents. Trades lower-temperature flexibility for superior fuel resistance.
Low ACN content (18–22%) for cold-flexibility to −65°F. Used in outdoor equipment, cold-weather hydraulics, and aerospace fuel systems where standard NBR would harden and lose sealing force at low temperature.
Compounds formulated to comply with FDA 21 CFR requirements for incidental food contact. Used in food processing equipment, beverage systems, and pharmaceutical machinery where fluid purity matters.
Optimized for static sealing applications requiring long service life without loss of sealing force. Minimizes permanent deformation under sustained compression — critical for face seals and flange joints.
Hydrogenated NBR for service above 250°F, sour gas (H₂S) exposure, or ozone-present environments where standard NBR falls short. Significant step up in heat and chemical resistance. Learn more →
Nitrile O-Ring Applications by Industry
NBR is the dominant o-ring material in any application involving oil or fuel. The industries below represent the core of nitrile o-ring demand — each with distinct performance requirements Wayne Rubber’s compound team understands in depth.
Static vs. Dynamic Nitrile O-Ring Applications
Static Seals
In static applications there is no relative motion between the o-ring and the mating surfaces. Face seals, flange seals, and threaded port seals are static applications. NBR performs very well in static service — compression set is the primary long-term concern, and Wayne Rubber’s low-compression-set grades maintain sealing force over extended service intervals.
Static NBR o-rings typically run 15–30% squeeze. Gland fill should stay between 65–85% to allow for thermal expansion without extrusion. Use the Gland Calculator to verify your groove dimensions.
Dynamic Seals
Dynamic applications involve reciprocating, oscillating, or rotary motion against the o-ring sealing surface. Hydraulic cylinder rod and piston seals are the most common NBR dynamic application. Dynamic squeeze is held tighter — typically 10–20% — to balance sealing effectiveness against friction and heat generation.
Surface finish is critical in dynamic applications: Parker ORD 5700 recommends 8–16 RMS on the sealing surface and 16–32 RMS on the groove walls to prevent premature wear while still maintaining a seal. NBR’s excellent abrasion resistance makes it particularly well-suited to reciprocating hydraulic service.
NBR vs. Other O-Ring Materials
NBR is the right first choice for oil, fuel, and hydraulic fluid service. This table helps confirm NBR is the correct specification for your environment — or identifies when a different compound would serve better.
| Property | NBR (Nitrile) | EPDM | FKM (Viton) | HNBR | Silicone |
|---|---|---|---|---|---|
| Petroleum Oils & Fuels | ✓ Excellent | ✗ Poor | ✓ Excellent | ✓ Excellent | ✗ Poor |
| Water & Steam | ▶ Good | ✓ Excellent | ▶ Good | ✓ Excellent | ✓ Excellent |
| Max. Temperature | +250°F (+121°C) | +300°F (+149°C) | +400°F (+204°C) | +300°F (+149°C) | +450°F (+232°C) |
| Low-Temp Flexibility | ✓ Good (to −40°F) | ✓ Excellent | ▶ Fair | ✓ Good | ✓ Excellent |
| Ozone & UV | ✗ Poor | ✓ Excellent | ✓ Excellent | ✓ Good | ✓ Excellent |
| Abrasion Resistance | ✓ Excellent | ▶ Good | ▶ Good | ✓ Excellent | ✗ Poor |
| Relative Cost | Low | Low – Medium | High | Medium – High | Medium – High |
Nitrile O-Ring Manufacturing at Wayne Rubber
Standard & Custom Sizes
Wayne Rubber manufactures nitrile o-rings in all standard AS568, ISO 3601, Metric, and JIS B2401 sizes, as well as fully custom dimensions for non-standard glands or unique equipment applications. Use the O-Ring Size Search to confirm your standard size, or contact us with your exact ID and cross-section for a custom quote.
In-House NBR Compounding
We develop and mix NBR compounds in-house across the full range of ACN contents and durometers. This lets us tailor oil resistance, low-temperature performance, compression set, and compliance characteristics to your exact specification — not just supply the nearest off-the-shelf grade. See our full nitrile rubber material page for compound data.
Compression & Injection Molding
O-rings are manufactured by compression or injection molding depending on size, volume, and tolerance requirements. Both processes are performed in-house at Wayne Rubber. Injection molding provides tighter dimensional control and minimal flash for critical sealing applications; compression molding is cost-effective for high-volume standard profiles.
Quality & Testing
Every NBR o-ring batch is dimensionally inspected and verified against material specifications before shipment. We support ASTM D2000, AS568, and ISO 3601 standards and provide material certifications and compliance documentation on request. Our testing capabilities include hardness, tensile, elongation, compression set, and fluid immersion testing.
Request a Quote for Custom Nitrile O-Rings
Provide your o-ring size (dash number, ID × CS, or drawing), quantity, and application details and Wayne Rubber will respond with material recommendations and pricing.