Viton O-Rings for AN Fittings: Sizing and Installation Tips

By DeatschWerks | Published: 2026-10-26

Category: How-to Guides

Learn how to choose the right Viton O-ring size for AN fittings and install them correctly to prevent leaks. Includes common mistakes and tips.

Quick Answer

For reliable sealing in AN fittings, choose Viton O-rings that match the fitting's dash size—such as 8AN for -8 fittings—and install them with proper lubrication and torque to avoid leaks.

Why Viton Over Buna-N?

Viton (FKM) offers superior resistance to heat, fuels, and oils compared to Buna-N (Nitrile). If your system runs hot or uses aggressive fluids, Viton is the safer choice. Buna-N is cheaper but may degrade faster under extreme conditions.

Sizing: Matching the O-Ring to Your AN Fitting

AN fittings use dash sizes (e.g., -6, -8) that correspond to the fitting's nominal outer diameter. The O-ring must match the groove and the fitting's boss. For 8AN fittings, use an 8AN O-ring. Using the wrong size can cause leaks or damage.

Step-by-Step Installation

Clean the fitting and groove: Remove any old O-ring and debris. Use a clean, lint-free cloth and a suitable solvent to ensure the groove is free of dirt or old sealant. A dirty groove is a common cause of leaks.
Lubricate the O-ring: Apply a thin layer of compatible lubricant (e.g., silicone grease) to the O-ring. This prevents pinching and helps it seat properly. Do not use petroleum-based lubricants with Viton unless specified.
Position the O-ring in the groove: Place the O-ring evenly in the groove, ensuring it is not twisted or rolled. It should sit flat and flush. A twisted O-ring will not seal correctly.
Install the fitting and torque to spec: Hand-tighten the fitting, then use a wrench to torque to the manufacturer's specification. Over-tightening can damage the O-ring or fitting. Check the torque spec for your specific fitting.
Pressure test for leaks: After installation, pressurize the system and inspect for leaks. If a leak appears, disassemble and check the O-ring for damage or misalignment. Catching a leak early saves time and prevents damage.

Product Spotlight

ORB 8AN Viton O-Ring (Pack Of 10): DeatschWerks ORB 8AN Viton O-Ring (Pack of 10) is designed for use with 8AN ORB fittings and is made from Viton for durability and fluid resistance. Keeping a pack on hand ensures you have the correct size for replacements or multi-point installations, reducing downtime.
ORB 8AN Viton O-Ring (Pack Of 10)