Nominal Size: 3/16" CS x 2-7/8" ID x 3-1/4" OD
The AS568-336 B70 Buna-N O-Ring (part number B70336) is a black, 70 durometer nitrile (NBR) O-Ring with a nominal size of 3/16" CS x 2-7/8" ID x 3-1/4" OD. It actually measures 0.210" CS x 2.850" ID x 3.270" OD, which is 5.33mm CS x 72.39mm ID x 83.06mm OD. It seals petroleum oils, hydraulic fluids, gasoline and cold water from -40F to +250F (-40C to +121C) and is stocked in the USA by The O-Ring Store LLC, an ISO 9001:2015 certified O-Ring distributor.
Keep the oil in and the leaks out with the AS568-336 Buna-N O-Ring. Black B70 nitrile is the everyday seal for maintenance crews, repair shops, engineers and OEMs who need dependable resistance to petroleum base oils and hydrocarbon fuels. Nitrile also brings excellent tensile strength and abrasion resistance, so the AS568-336 holds up to the wear and tear of real equipment and is easy to find and replace when service time comes around.
Operating Temperature
-40F to +250F (-40C to +121C)
The B70 compound used for the AS568-336 is rated for an operating temperature of -40F to +250F (-40C to +121C), and that is the range to design around.
Material and Performance Details
Buna-N, also known as Nitrile or NBR, is a copolymer of butadiene and acrylonitrile and is the most commonly used elastomer for sealing products. More than 50% of the O-Rings sold are nitrile. B70 is a general purpose, sulfur-cured nitrile compound, black in color and 70 durometer on the Shore A scale. That 70 durometer hardness is the middle-of-the-road standard: soft enough to seal well and firm enough to resist wear. The compound is exceptionally resistant to petroleum base oils and hydrocarbon fuels and performs well with most dilute acids, silicone oils and lubricants and in water applications.
B70 Buna-N is recommended for:
- General purpose sealing
- Petroleum oils and fluids
- Gasoline
- Hydraulic fluids
- L.P. gases
- Cold water
- Silicone greases and oils
- Di-ester base lubricants (MIL-L-7808)
- Ethylene glycol base fluids (Hydrolubes)
- Most dilute acids
B70 Buna-N is not recommended for:
- Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene)
- Nitro hydrocarbons (nitrobenzene, aniline)
- Phosphate ester hydraulic fluids (Skydrol, Fyrquel, Pydraul)
- Ketones (MEK, acetone)
- Aromatic hydrocarbons
- Strong acids
- Automotive brake fluid
- Ozone
- Sunlight and UV
- Weather
Because ozone, sunlight and weather are on the not-recommended list, keep spare AS568-336 O-Rings in their bag, out of direct light and away from electric motors and welders until they go in. For outdoor exposure, brake fluid, Skydrol, MEK or acetone, call us and we will point you to a compound built for that job.
Sizes and Measurements (CS x ID x OD)
- Nominal: 3/16" CS x 2-7/8" ID x 3-1/4" OD
- Actual: 0.210" CS x 2.850" ID x 3.270" OD
- Metric: 5.33mm CS x 72.39mm ID x 83.06mm OD
- Part Number: B70336
- AS568 Dash Number: -336 (AS568-336)
- Size Series: AS568 -300 series (3/16" nominal cross-section)
- Also listed as size 2-336 in many O-Ring catalogs
- Next size down in this cross-section: AS568-335 (part number B70335)
- Next size up in this cross-section: AS568-337 (part number B70337)
Nominal vs. actual size: The nominal size is the rounded fractional name people use to talk about and order the part. The actual size is what the O-Ring really measures, and the two are not the same. On the AS568-336, the nominal cross-section is 3/16" (0.188") and the actual cross-section is 0.210". The nominal ID is 2-7/8" (2.875") and the actual ID is 2.850". Use the actual numbers for groove design and for matching an old seal.
Outside diameter is figured from the actual sizes as ID plus two times the cross-section. Metric numbers are the actual inch sizes converted at 25.4mm per inch.
Applications and Use Cases
The -300 series carries a 3/16" nominal cross-section. These heavier sizes go on larger cylinders, pump housings, hydraulic flanges, covers and heavy equipment where a thicker seal is called for. In B70 Buna-N, the AS568-336 is a natural fit for hydraulic and pneumatic motors, cylinders, pumps and valves, along with fuel and lubrication systems, L.P. gas equipment, cold water service and anywhere silicone greases or petroleum oils are present.
Key Specifications
- Material: Buna-N (Nitrile, NBR), B70 general purpose sulfur-cured compound
- Durometer: 70 Shore A
- Color: Black
- Operating Temperature: -40F to +250F (-40C to +121C)
- FDA: No
- ASTM D2000-99 Grade M2BG714 B14 EA14 EF11 EF21 EO14 EO34 Z1, where Z1 = TR10 = -31.9C (-25.4F)
- Designed to meet or exceed the properties of these popular Buna Nitrile compounds: N674-70, N100-70, 7507, B46-70, 4200-70, H14327, 4700-70 and 366Y
- Standard: AS568, dash number -336
- Compound data sheet: linked on this page
Reading the ASTM line call: ASTM D2000 is the standard way to spell out what a rubber compound has to pass. For B70 it means the compound is heat aged at 100C (212F), held to 70 durometer and a minimum tensile strength of 14 MPa (about 2,030 psi) and tested for compression set, water resistance, fuel resistance in ASTM Fuels A and B and oil resistance in ASTM No. 1 and IRM 903 oils. The Z1 callout adds a low temperature retraction test, with TR10 at -31.9C (-25.4F).
Why Buy from The O-Ring Store LLC
The O-Ring Store LLC is an ISO 9001:2015 certified distributor with USA-based stock for fast delivery. Most in-stock items ship the same day. We offer custom sizes, including precision-spliced vulcanized O-Rings made here in the U.S., full lot traceability and documentation on request and real technical help from people with decades of sealing experience. Every order is verified through our Olypsys® scan-based quality system before it ships. Competitive pricing with no compromise on quality. We make getting O-Rings easy!
Frequently Asked Questions
What size is the AS568-336 O-Ring?
The AS568-336 O-Ring has a nominal size of 3/16" CS x 2-7/8" ID x 3-1/4" OD. Its actual size is 0.210" CS x 2.850" ID x 3.270" OD, or 5.33mm CS x 72.39mm ID x 83.06mm OD, listed as cross-section x inside diameter x outside diameter.
Why are the nominal and actual sizes of the AS568-336 different?
Nominal is the rounded fractional name for the size (3/16" CS x 2-7/8" ID x 3-1/4" OD). Actual is what the AS568-336 really measures (0.210" CS x 2.850" ID x 3.270" OD). Always use the actual size for groove design and for matching a replacement.
What temperature range can the AS568-336 Buna-N O-Ring handle?
The AS568-336 in B70 Buna-N is rated for an operating temperature of -40F to +250F (-40C to +121C).
Is the AS568-336 Buna-N O-Ring good for hydraulic oil and gasoline?
Yes. B70 Buna-N is exceptionally resistant to petroleum base oils and hydrocarbon fuels and is recommended for hydraulic fluids, gasoline, L.P. gases, silicone greases and oils, di-ester base lubricants (MIL-L-7808) and ethylene glycol base fluids.
What should I keep the AS568-336 Buna-N O-Ring away from?
B70 Buna-N is not recommended for automotive brake fluid, phosphate ester hydraulic fluids such as Skydrol, Fyrquel and Pydraul, ketones such as MEK and acetone, aromatic hydrocarbons, halogenated hydrocarbons, nitro hydrocarbons, strong acids or long exposure to ozone, sunlight, UV and weather.
Is the B70336 O-Ring FDA compliant for food contact?
No. B70 is a general purpose industrial nitrile compound and is not an FDA food-contact compound. For food and beverage service, ask us about our FDA-grade compounds such as White FDA Buna-N.
What O-Ring compounds does B70 Buna-N replace?
B70 is designed to meet or exceed the properties of these popular Buna Nitrile compounds: N674-70, N100-70, 7507, B46-70, 4200-70, H14327, 4700-70 and 366Y. If your print calls for one of those in size AS568-336, part number B70336 is the match to check.
