Nominal Size: Tube Size 7/8"
The AS568-914 B70 Buna-N O-Ring (part number B70914) is a black, 70 durometer nitrile (NBR) boss O-Ring for 7/8" tube size straight thread fittings. It actually measures 0.116" CS x 1.047" ID x 1.279" OD, which is 2.95mm CS x 26.59mm ID x 32.49mm 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 AS568-914 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 AS568-914 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 AS568-914 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 AS568-914 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: Tube Size 7/8"
- Actual: 0.116" CS x 1.047" ID x 1.279" OD
- Metric: 2.95mm CS x 26.59mm ID x 32.49mm OD
- Part Number: B70914
- AS568 Dash Number: -914 (AS568-914)
- Size Series: AS568 -900 series (straight thread boss)
- Also listed as size 3-914 in many O-Ring catalogs
- Next size down in the boss series: AS568-913 (part number B70913)
- Next size up in the boss series: AS568-916 (part number B70916)
Nominal vs. actual size: Boss O-Rings are named for the tube size of the fitting they serve, not for the O-Ring's own measurements. The 7/8" tube size calls for an O-Ring that actually measures 0.116" CS x 1.047" ID x 1.279" OD (2.95mm CS x 26.59mm ID x 32.49mm OD). Match the actual numbers when you are checking an old seal or a port.
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 -900 series is built for straight thread O-Ring boss (ORB) ports and tube fittings. The O-Ring sits on the fitting, seats in the chamfer of the port and seals when the fitting is tightened down. These sizes are all over hydraulic pumps, motors, valves, manifolds and cylinders. In B70 Buna-N, the AS568-914 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 -914
- 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 AS568-914 O-Ring?
The AS568-914 is a boss O-Ring for 7/8" tube size straight thread fittings. It actually measures 0.116" CS x 1.047" ID x 1.279" OD, or 2.95mm CS x 26.59mm ID x 32.49mm OD, listed as cross-section x inside diameter x outside diameter.
What fitting does the AS568-914 O-Ring fit?
The AS568-914 is sized for 7/8" tube size straight thread O-Ring boss (ORB) ports and fittings. It sits on the fitting and seals against the chamfer of the port when the fitting is tightened.
What temperature range can the AS568-914 Buna-N O-Ring handle?
The AS568-914 in B70 Buna-N is rated for an operating temperature of -40F to +250F (-40C to +121C).
Is the AS568-914 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 AS568-914 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 B70914 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 AS568-914, part number B70914 is the match to check.
