ASTM, or the American Society for Testing and Materials, is an organization that develops and publishes technical standards for a wide range of materials, products, systems, and services. One such standard is the ASTM O-Ring Specifications, which are used to classify and specify the properties of O-Rings, a type of sealing ring used in various industrial applications.
Understanding and reading the ASTM O-Ring Specifications can be broken down into several key areas:
- Material: ASTM has specifications for different rubber materials used in the manufacture of O-Rings. These include Nitrile (Buna-N), Viton (FKM), Silicone, EPDM, and many more. Each material has different properties and is suited for different applications and environments.
- Size: ASTM has a standard system for O-Ring sizes, known as the AS568 standard. This standard classifies O-Rings into five categories: 001-178 (standard sizes), 201-349 (sizes for boss tube fittings), 377-662 (larger diameters), 901-932 (backup rings), and 1001-1092 (quad-ring seals).
- Durometer hardness: The hardness of the O-Ring material is measured on the durometer scale. ASTM D1414 (for rubber) and ASTM D2240 (for plastics and soft rubbers) are the relevant standards. The hardness is usually measured as a number followed by the letter "A" or "D".
- Temperature Range: Each O-Ring material has a specified temperature range within which it performs optimally. Operating outside this range can lead to failure of the seal.
- Chemical Resistance: ASTM has guides on the chemical resistance of different O-Ring materials. These guides show which materials are suitable for use with specific chemicals.
- Performance Properties: ASTM D2000 is the standard classification system for rubber materials in automotive applications, based on resistance to heat, compression set, cold, and other factors.
When reading the ASTM O-Ring Specifications, you would typically see a series of letters and numbers that specify the material, hardness, and performance properties of the O-Ring. For example, a classification might look like this: "ASTM D2000 M2HK 707 A1-10, B38, C12, EF31, EO88, F15, Z1".
This can be broken down as follows:
- D2000: This indicates that the classification is based on the D2000 standard.
- M2HK: This is the "line call-out". "M" means that it's based on SI units. "2" is the type (based on resistance to heat aging). "H" is the class (based on resistance to oil and heat). "K" is the grade (based on physical properties).
- 707: This is the hardness (70) and tensile strength (7).
- A1-10, B38, C12, EF31, EO88, F15, Z1: These are the "suffix requirements", specifying additional properties like heat resistance (A), compression set (B), cold resistance (C), etc.
Overall, understanding and reading the ASTM O-Ring Specifications involves a good knowledge of the materials and properties of O-Rings, as well as the various codes and classifications used by the ASTM. It's important to use the correct specifications for the application to ensure optimal performance and longevity of the O-Ring.
Here is an example of our B70 Standard Grade ASTM guideline.
ASTM D2000-99 Grade: M2BG714 B14 EA14 EF11 EF21 EO14 EO34 Z1 (TR10 = –31.9°C)
1. ASTM D2000-99
- ASTM D2000 is the “Standard Classification System for Rubber Products in Automotive Applications.”
- The “99” indicates the revision year (1999 standard).
This spec defines rubber materials by performance rather than chemistry, so different compounds (from different suppliers) can meet the same callout if they pass all required tests.
2. M2BG
- M = General classification (used for non-oil resistant materials in automotive service).
- 2 = Heat resistance requirement (tested at 1000 hours at 100°C).
- B = Material type → Nitrile (NBR, acrylonitrile-butadiene rubber).
- G = Oil resistance → Good resistance to oil and fuel.
So, this is a Nitrile rubber designed for oil resistance, with automotive-grade heat aging performance.
3. 714
This part defines durometer and tensile properties:
- 7 = Hardness → 70 Shore A ± 5.
- 1 = Tensile strength → 14 MPa minimum (≈ 2000 psi).
- 4 = Elongation → 250% minimum.
This tells us it’s a 70 durometer Nitrile compound with good tensile strength and flexibility.
4. Suffix Requirements
Suffixes show additional tests the compound must meet:
- B14: Heat aging resistance.
- 1000 hours @ 100°C → max hardness change ±15, tensile strength ±30%, elongation ±50%.
- EA14: Resistance to aqueous fluids (like coolants, brake fluids).
- 70 hours at 100°C in test fluid.
- EF11 & EF21: Resistance to fuels.
- EF11 → Fuel C (standard fuel test fluid).
- EF21 → Fuel C with higher ethanol content.
- EO14 & EO34: Resistance to oils.
- EO14 → ASTM Oil No. 1 (non-aggressive oil).
- EO34 → ASTM Oil No. 3 (more aggressive oil, high swell potential).
- Z1 (TR-10 = –31.9°C): This is a special requirement noted by the designer.
- TR-10 is the Temperature Retraction test, measuring low-temperature flexibility.
- TR-10 = –31.9°C means the rubber remains flexible down to about –32°C, which is excellent low-temperature performance for NBR.
Summary for Customers
This compound is a 70-durometer Nitrile (NBR) designed for automotive-grade sealing applications where oil, fuel, and coolant resistance are required.
Key Benefits for You:
- Reliable in Oils & Fuels – tested against multiple oils and fuel blends, ensuring durability in engine, hydraulic, and fuel systems.
- Wide Temperature Range – flexible at cold temps down to –32°C and stable in heat aging up to 100°C for long service life.
- Balanced Strength & Flexibility – 2000+ psi tensile and 250% elongation means tough yet not brittle.
- Automotive-Grade Standardization – you can source this spec from multiple qualified suppliers without losing performance.
- ISO9001-Backed Quality – ensures consistent performance, traceability, and customer confidence.