3.5mm CS X 21.7mm ID (NBR) Buna-N 90 Duro Metric O-Ring (JIS P22A)

3.5mm CS x 21.7mm ID x 28.7mm OD Buna-N 90 Durometer Metric O-Ring (JIS P22A)

Part number H3.50X021.7 is a black Buna-N (Nitrile, NBR) 90 durometer metric O-Ring with a 3.50mm cross-section, a 21.70mm inside diameter and a 28.70mm outside diameter. It is the standard JIS B 2401 P22A size. It is made to ISO 3601-1 dimensional tolerances and ISO 3601-3 Grade N surface quality and is sold by The O-Ring Store LLC, an ISO 9001:2015 certified O-Ring distributor.

When system pressure climbs, a 70 durometer seal can get pushed into the clearance gap and start to nibble and tear. This 3.5mm CS x 21.7mm ID O-Ring is the harder 90 durometer version of Buna-N, so it holds its shape in the gland and keeps sealing in higher pressure hydraulic and pneumatic service. It is a good pick for worn hardware with opened up clearances and for metric equipment built in Europe and Asia.

Operating Temperature: -40°F to +250°F (-40°C to +121°C)

Material and Performance Details

Nitrile, also known as Buna-N or NBR, is a copolymer of butadiene and acrylonitrile. It is the most commonly used elastomer for sealing, and more than half of all O-Rings sold are Nitrile. It is exceptionally resistant to petroleum base oils and hydrocarbon fuels and it has excellent tensile strength and abrasion resistance. It also performs well with most dilute acids, silicone oils and lubricants and in water applications. This compound is 90 Shore A durometer (plus or minus 5 points) and black. The harder 90 durometer grade gives better extrusion resistance than a 70 durometer, so it needs a good surface finish and a properly sized gland to seat. Check your groove dimensions before stepping up from a 70.

Buna-N 90 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)

Buna-N 90 is not recommended for:

• Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene)
• Nitro hydrocarbons (nitrobenzene, aniline)
• Phosphate ester hydraulic fluids (Skydrol, Fyrquel, Pydraul)
• Ketones (MEK, acetone)
• Ozone
• Sunlight and UV
• Weather
• Strong acids
• Automotive brake fluid

Sizes and Measurements

• Nominal size: JIS P22A
• Actual: 0.138" CS x 0.854" ID x 1.130" OD
• Metric: 3.50mm CS x 21.70mm ID x 28.70mm OD
• Part Number: H3.50X021.7
• Standard size references: JIS B 2401 P22A
• Tolerances: ISO 3601-1

Applications and Use Cases

The 3.5mm CS x 21.7mm ID Buna-N 90 O-Ring goes to work in hydraulic and pneumatic motors, cylinders, pumps and valves, which is where most Nitrile O-Rings end up. Maintenance shops, equipment builders and OEMs reach for the 90 durometer when pressure is high, when a 70 durometer seal keeps extruding or when a metric machine calls for a harder seal from the factory.

• Hydraulic cylinders and actuators running petroleum hydraulic fluid
• Hydraulic and pneumatic motors
• Pump housings, covers and shaft areas in oil service
• Control valves and valve bodies on metric equipment
• Metric hydraulic fittings, adapters and manifolds
• Gasoline, diesel and L.P. gas equipment
• Lubrication and grease systems using petroleum or silicone greases

Key Specifications

• Material: Buna-N (Nitrile, NBR)
• Hardness: 90 Shore A, plus or minus 5
• Color: Black
• Temperature Range: -40°F to +250°F (-40°C to +121°C)
• Dimensional Tolerances: ISO 3601-1
• Surface Quality: ISO 3601-3 Grade N
• Inspection: AQL 1.0
• Size: 3.50mm CS x 21.70mm ID x 28.70mm OD

Why Buy from The O-Ring Store LLC

The O-Ring Store LLC is an ISO 9001:2015 certified O-Ring distributor with stock in Clarkston, Washington. In-stock orders usually ship the same day, and we carry a deep line of metric sizes so you are not stuck waiting on a seal from overseas. Every order is checked through our Olypsys® scan-based quality system before it ships, lot traceability and documentation are available on request, and our staff has decades of sealing experience to help you pick the right part. We make getting O-Rings easy!

Frequently Asked Questions

Q: What are the exact dimensions of the 3.5mm CS x 21.7mm ID O-Ring? A: The cross-section is 3.50mm (0.138"), the inside diameter is 21.70mm (0.854") and the outside diameter is 28.70mm (1.130"). The outside diameter is the inside diameter plus two cross-sections: 21.70mm + 3.50mm + 3.50mm = 28.70mm.

Q: Will this Buna-N O-Ring work with brake fluid or Skydrol? A: No. Buna-N is not recommended for automotive brake fluid or phosphate ester hydraulic fluids like Skydrol, Fyrquel and Pydraul. It is the right choice for petroleum oils, hydraulic fluids, gasoline, L.P. gases and cold water.

Q: Why is the JIS P22A O-Ring not exactly 22mm? A: P22A is the nominal JIS B 2401 size name. The actual O-Ring measures 3.50mm CS x 21.70mm ID x 28.70mm OD. Nominal and actual are two different numbers, so always order by the actual measurements when you are matching an old seal.