Replacement O-Rings for EFI Fittings: Size Guide
By DeatschWerks | Published: 2026-10-18
Category: Buying Guides
Learn how to match replacement O-rings for EFI fittings by size, material, and port type. Get practical selection rules for 1/4, 5/16, and ORB sizes.
Quick Answer
Choose replacement O-rings for EFI fittings by matching the fitting size (1/4 or 5/16 inch) or the ORB port size (6AN or 10AN), and confirm the material suits your fuel type and temperature range. For most fuel injection systems, Viton O-rings offer broad compatibility, but always verify the exact fitting model before ordering.
Why Size and Material Matter
O-rings are the sealing backbone of EFI plumbing. A wrong size leads to leaks or fitting damage; the wrong material can swell, harden, or degrade in fuel. DeatschWerks offers two common sizing systems: fractional inch sizes for female EFI fittings (1/4 and 5/16 inch) and AN-style ORB ports (6AN and 10AN). Knowing which system your fitting uses is the first step.
Material choice is equally important. Standard nitrile (Buna-N) works for many applications, but Viton (FKM) resists higher temperatures and a broader range of fuels and chemicals. If your system runs E85, race fuel, or high under-hood temperatures, Viton is often the safer pick.
Fractional vs. ORB Sizing
Fractional sizes (1/4, 5/16) refer to the tubing or fitting outer diameter in inches, common on push-on or barbed EFI fittings. ORB sizes (6AN, 10AN) refer to the O-ring boss port thread size, typical on AN fittings with a machined boss. They are not interchangeable—you cannot use a 1/4-inch O-ring on a 6AN port.
Check your fitting's spec sheet or measure the groove diameter. If you are replacing an existing O-ring, match the old one's dimensions and material. When in doubt, consult the fitting manufacturer's cross-reference.
Decision Rules for Choosing Replacement O-Rings
- Identify the fitting type: Determine if your fitting uses a fractional inch size (1/4 or 5/16) or an ORB port (6AN or 10AN). Check the fitting body or the manufacturer's spec. If you cannot identify the size, measure the groove diameter or consult the fitting's documentation.
- Match the exact size: For fractional fittings, choose the O-ring that matches the inch size (e.g., 1/4 or 5/16). For ORB ports, match the AN size (6AN or 10AN). Do not mix systems. Using the wrong size will cause leaks or damage—double-check before ordering.
- Select the material based on fuel and temperature: If your system uses standard gasoline and moderate temperatures, nitrile may suffice. For E85, race fuel, or high heat, choose Viton for better resistance. When unsure, Viton is the safer choice for most EFI applications.
- Verify fitting model compatibility: For female EFI fittings, confirm the O-ring is designed for your specific fitting model (e.g., 6-02-0121 or 6-02-0143). Some O-rings are model-specific. If your fitting model is not listed, contact the manufacturer or measure the O-ring groove.
- Consider buying a pack for spares: O-rings are wear items. A 10-pack ensures you have replacements on hand for future maintenance, avoiding downtime. If you have multiple fittings or plan future work, a pack is cost-effective.
Product Options at a Glance
- Replacement O-Rings for 1/4 Inch Female EFI Fittings (6-02-0120): Direct replacement sealing component for compatible 1/4 inch female EFI fittings. If your system uses 1/4-inch female EFI fittings, this O-ring is sized to match that specific fitting, so you avoid guesswork.
Replacement O-Rings for 1/4 Inch Female EFI Fittings (6-02-0120) - Replacement O-Rings for 5/16 Inch Female EFI Fittings (6-02-0121, 6-02-0143): Designed for 5/16 inch female EFI fittings, specifically models 6-02-0121 and 6-02-0143. This O-ring is tailored to those exact fitting models, ensuring a proper seal without needing to measure the groove yourself.
Replacement O-Rings for 5/16 Inch Female EFI Fittings (6-02-0121, 6-02-0143) - ORB 10AN Viton O-Ring (Pack Of 10): Pack of 10 Viton O-rings sized for 10AN fittings. Viton offers high heat and chemical resistance, and the 10-pack gives you spares for multiple installations or future replacements.
- ORB 6AN Viton O-Ring (Pack Of 10): Pack of 10 Viton O-rings sized for 6AN fittings. Ideal for 6AN ORB ports, the Viton material suits demanding fuel systems, and the 10-pack covers several fittings.
Who Should Use Which O-Ring
Best for
- 1/4-inch female EFI fittings: use the 1/4-inch replacement O-ring (product 2680588)
- 5/16-inch female EFI fittings (models 6-02-0121 or 6-02-0143): use the 5/16-inch replacement O-ring (product 2680587)
- 6AN ORB ports needing high-temperature resistance: use the 6AN Viton pack (product 2680582)
- 10AN ORB ports needing high-temperature resistance: use the 10AN Viton pack (product 2680586)
Not for
- Systems with unknown fitting sizes—measure first
- Applications requiring non-Viton materials like PTFE or silicone (not offered here)
- ORB ports that are not 6AN or 10AN (e.g., -8AN)
