Freudenberg N888: Low-Temp Aerospace Nitrile O-Ring (70 Duro NBR)
Freudenberg N888 is a 70 durometer low-temperature nitrile (NBR/Buna-N) O-Ring for aerospace: flexible to -65°F, qualified to MIL-G-5514 and SAE AS5440, built to AS28775, MS28775, and MS28784.
Freudenberg N888 is a 70 durometer, low-temperature nitrile (NBR / Buna-N) O-Ring compound built for aerospace. It is black, developed by Freudenberg-NOK Sealing Technologies, and it stays flexible all the way down to -65°F (-54°C) while handling temperatures up to +250°F (+121°C). N888 is qualified to MIL-G-5514 and SAE AS5440, and it resists petroleum-based hydraulic fluids per MIL-PRF-5606, MIL-PRF-87257, and MIL-PRF-83282. You will find it sealing landing gear, flight controls, and braking systems on aircraft.
What is Freudenberg N888?
N888 is not general-purpose Buna-N. It is a specialized nitrile compound engineered for the cold and the pressure of flight. Standard nitrile gets stiff and brittle in the cold, which is exactly where a hydraulic seal cannot afford to fail. N888 is formulated to stay soft and sealing at -65°F, which is why it has become a trusted aerospace grade for aircraft hydraulic systems and the equipment that supports them.
The compound is a 70 Shore A nitrile, so it hits the durometer most hydraulic O-Ring grooves are designed around. It carries the oil and fuel resistance nitrile is known for, plus the low-temperature flexibility and specification pedigree that aerospace work demands.
The short version: N888 is what you reach for when a standard Buna-N O-Ring would fail in the cold. Same nitrile family, aerospace-grade formulation, qualified for aircraft hydraulics.
Why low temperature is the whole point
Aircraft operate at altitude, where temperatures drop hard. A seal that turns rigid in the cold loses its ability to spring back and fill the groove, and that is when leaks start. N888 is built to keep its flexibility down to -65°F, so it holds a seal through the cold soak of high-altitude flight and cold-weather ground operations. That single property is the reason the compound exists.
N888 technical specifications
The values below come from the published N888 material data sheet, tested to ASTM methods on standard 2mm sheet. Finished O-Rings can vary slightly based on part geometry and cure, which is normal for any molded elastomer.
| Property | Test method | Value |
|---|---|---|
| Material | Nitrile (NBR / Buna-N) | 70 NBR N888 |
| Color | Visual | Black |
| Hardness | ASTM D2240, Shore A | 70 Shore A |
| Density | ASTM D297 | 1.17 g/cm³ |
| Modulus at 100% | ASTM D412, Die C | 630 psi |
| Tensile strength | ASTM D412, Die C | 2159 psi |
| Elongation at break | ASTM D412, Die C | 271% |
| Service temperature | Continuous | -65°F to +250°F |
Military and aerospace specifications
N888 earns its place on aircraft drawings because it is built and tested against the specifications aerospace engineers call out. Here is what the compound is qualified and recognized for:
- MIL-G-5514 and SAE AS5440: the gland design and hydraulic packing standards N888 O-Rings are built to serve.
- MIL-PRF-5606: resistant to this petroleum-based hydraulic fluid, the classic mineral-oil aircraft hydraulic fluid.
- MIL-PRF-87257: resistant to this synthetic hydrocarbon-based fire-resistant hydraulic fluid.
- MIL-PRF-83282: resistant to this synthetic hydrocarbon-based hydraulic fluid used across military aircraft.
Because it covers the common aircraft hydraulic fluids, a single N888 grade can seal across a lot of different systems without switching compounds. For the wider world of military O-Ring callouts, see the mil-spec reference.
The three O-Ring norms: AS28775, MS28775, MS28784
Freudenberg lists N888 O-Rings under three norms. They are not three different rings. They are three specification numbers that call out the same aerospace O-Ring sizes, which is why you see all three cross-referenced together on catalogs and bills of material.
| Norm | Role | What it is |
|---|---|---|
| AS28775 | Active SAE standard | The current SAE Aerospace Standard for O-Rings in aircraft hydraulic and pneumatic systems. The living successor to the older military MS28775, defining the sizes and tolerances in use today. |
| MS28775 | Legacy military standard | The long-standing military standard for hydraulic packing O-Rings. It still appears on countless drawings and part numbers, so buyers ask for it by name even though AS28775 now carries it forward. |
| MS28784 | Legacy cross-reference | A companion military O-Ring standard listed alongside MS28775 for the same sizes. It shows up as an interchangeable cross-reference on aerospace and defense part lists. |
Buyer tip: If your drawing calls out MS28775 or MS28784 in a nitrile grade, a 70 durometer N888 O-Ring in the matching AS568 dash size is the low-temperature aerospace answer.
Where N888 O-Rings are used
N888 was made for aircraft hydraulics, and that is where it earns its keep. The most common home for it is the hydraulic systems that move and control an aircraft, plus the parts that take a beating from motion and shock.
Beyond the airframe, N888 is a fit for shock absorbers and struts, emergency systems, and non-aircraft applications like maintenance and ground support equipment that still require aerospace-grade certification.
How N888 O-Rings are numbered
If you have seen a part number like 62AS568-214 N888, that is Freudenberg’s legacy item format. Reading it left to right: 62 is Freudenberg’s series prefix, AS568-214 is the standard inch dash size, and N888 is the compound. So the number tells you the size and the material in one string.
Because these are AS568 dash sizes, cross-referencing is straightforward. A given dash number lines up with the same MS28775 and MS28784 size, so you can match a drawing callout to the right N888 O-Ring by dash number alone. Look any dash up in the Master O-Ring Size Chart.
Frequently asked questions
What is Freudenberg N888?
N888 is a 70 durometer, low-temperature nitrile (NBR / Buna-N) O-Ring compound developed by Freudenberg-NOK Sealing Technologies for aerospace. It is black and stays flexible down to -65°F, which makes it a go-to for aircraft hydraulic systems.
What temperature range does N888 handle?
N888 has a continuous service range of -65°F to +250°F (-54°C to +121°C). The low-temperature end is the reason it is chosen over standard nitrile, since it keeps sealing where ordinary Buna-N would stiffen and leak.
Is N888 the same as standard Buna-N or B70?
N888 is a nitrile at 70 durometer, so it shares the family and the hardness, but it is a specialized low-temperature aerospace grade rather than general-purpose Buna-N. It carries aerospace qualifications and cold flexibility that standard nitrile does not.
What is the difference between AS28775, MS28775, and MS28784?
They are specification numbers that call out the same aerospace O-Ring sizes. AS28775 is the active SAE standard, MS28775 is the legacy military standard it replaced, and MS28784 is a companion military standard cross-referenced for the same sizes. One N888 O-Ring in the matching dash size can satisfy all three callouts.
What hydraulic fluids is N888 compatible with?
N888 resists petroleum-based aircraft hydraulic fluids per MIL-PRF-5606, MIL-PRF-87257, and MIL-PRF-83282. That covers the common mineral-oil and synthetic hydrocarbon hydraulic fluids used across aircraft.
Where can I buy Freudenberg N888 O-Rings?
The O-Ring Store LLC stocks N888 O-Rings across AS568 sizes and ships them fast. If you have a dash number, an MS28775 or MS28784 callout, or a full drawing, we can match the right size and get it out the door.
Why buy N888 O-Rings from The O-Ring Store LLC
Aerospace sealing is no place to guess. When you order N888 from us, you get more than a part in a bag:
- ISO 9001:2015 certified quality, so the O-Ring you order is the O-Ring you get. See our Certificate of Conformance, cure date, and lot traceability.
- Olypsys® scan-based verification checks the right part into every order for traceability you can stand behind.
- Full AS568 size coverage in N888, matched to your dash number or MS28775 / MS28784 callout.
- Real people in Clarkston, Washington who know seals and answer the phone.
- Fast shipping and honest help, because getting O-Rings should be the easy part of your day.
Shop N888 O-Rings at The O-Ring Store, ISO 9001:2015 certified, CAGE Code 72PR0.
Technical values are drawn from the published 70 NBR N888 material data sheet and are typical results on standard ASTM test pieces. Finished O-Ring performance can vary with part geometry and application. Confirm suitability for your specific service before use. Freudenberg and N888 are marks of their respective owner and are referenced here for identification of the compound we supply.
