Direct answer: NBR is often a practical starting point for many petroleum-oil, grease, and conventional hydraulic-fluid applications. FKM is often compared for some fuels, hotter oil, and more demanding fluid exposure. The final choice depends on the exact fluid, additives, temperature, pressure, motion, groove, hardness, and exposure time.
Why the exact fluid matters
“Oil,” “fuel,” and “hydraulic fluid” are broad categories. Different formulations and additives can produce different results. Identify the product name or fluid specification whenever possible.
NBR as a common starting point
NBR is widely used in many oil and grease applications and is often economical for general maintenance. It should not be assumed suitable for every fuel, synthetic fluid, outdoor environment, or high-temperature condition.
When FKM should be compared
FKM is often reviewed when fuel exposure, higher temperature, or more demanding oil service is involved. It is not automatically compatible with every fuel, coolant, chemical, or hydraulic fluid.
Hydraulic systems require more than material selection
- Hydraulic fluid type and additives
- Operating and peak pressure
- Minimum and maximum temperature
- Static or dynamic seal
- Groove clearance and extrusion risk
- Required hardness
- Surface condition and installation method
Do not choose by colour or equipment name
A black O-ring may be NBR, FKM, EPDM, or another compound. Equipment labels such as “pump,” “engine,” or “hydraulic fitting” do not identify the fluid or the required compound.
Choose the buying path
- Exact size, material, hardness, and fluid confirmed: search the exact specification or browse small packs.
- Fluid, temperature, pressure, or material uncertain: review the Chemical Compatibility Guide and use Bulk Quote.
- Drawing, sample, special compound, unusual size, or larger quantity: submit the complete requirement for review.
What to include in a request
- ID and CS
- Material and hardness if known
- Exact fuel, oil, or hydraulic fluid
- Temperature and pressure
- Static or dynamic motion
- Quantity
- Drawing, photo, sample, or part number
FAQ
What O-ring material is best for oil?
NBR is a common starting point for many petroleum oils and greases, but the exact oil, temperature, and operating conditions must be checked.
What material should I check for fuel?
FKM is often compared for fuel-related service, but fuel formulation, temperature, and compound-specific compatibility still matter.
Are hydraulic O-rings always NBR?
No. The correct material depends on the hydraulic fluid, additives, temperature, pressure, motion, and equipment specification.
Can I identify the material by colour?
No. Colour is not proof of material or compatibility.
Technical reference: Parker O-Ring Handbook. See also the OXXRing sources and review policy.
