MS29512-04 – Hydrocarbon Fuel Resistant O-Ring
Available now through the AirParts Aero marketplace.
Overview Section
The MS29512-04 is a high-performance Nitrile (Buna-N) O-ring specifically engineered for sealing straight-thread tube fittings in aircraft fuel and oil systems. Manufactured to the MS29512 military specification, this O-ring is the industry standard for applications involving aromatic and non-aromatic hydrocarbon fluids.
The -04 dash number indicates its compatibility with -4 size (1/4") aerospace fluid fittings. Unlike standard industrial Nitrile, MS29512 O-rings are formulated to resist the "shrinkage" and hardening that can occur when exposed to high-octane aviation gasolines and jet fuels, ensuring a leak-proof seal over long service intervals.
Key Features Section
Hydrocarbon Resistance: Specifically formulated for constant immersion in Jet A/A-1, JP-8, and 100LL Avgas, as well as MIL-L-6082 and MIL-L-22851 piston engine oils.
Optimized for Straight Threads: Designed to fit the "boss" of AS5202 (formerly MS33649) internal straight-thread ports, providing a superior seal compared to tapered pipe threads.
Medium-Hardness Nitrile (90 Shore A): Features a high durometer rating to resist "extrusion" under pressure and "nibbling" during the installation of high-torque fittings.
Low-Temperature Flexibility: Engineered to remain supple and maintain a seal at temperatures as low as -65°F (-54°C), a critical requirement for high-altitude flight.
Precision Geometry: Manufactured with zero flash or parting-line imperfections, preventing "bypass" leaks at the molecular level.
Color Coded/Marked: Usually identified by a blue dot or stripe (depending on the manufacturer) to distinguish it from similar-looking hydraulic or high-heat O-rings.
Technical Specifications Section
| Specification | Detail |
| Part Number | MS29512-04 |
| Material | Nitrile (Buna-N / NBR) |
| Fits Fitting Size | -4 (1/4 inch) |
| Inside Diameter (ID) | 0.351 in (Nominal) |
| Cross-Section (W) | 0.072 in (Nominal) |
| Hardness | 90 Shore A Durometer |
| Operating Temp | -65°F to +250°F (-54°C to +121°C) |
Aircraft Compatibility Section
The MS29512-04 is a fundamental sealing component across the general aviation and commercial fleet:
Cessna/Piper/Beechcraft: Used in fuel selector valves, fuel strainer bowls (gascolators), and engine-driven fuel pump fittings.
Lycoming & Continental Engines: Found in oil cooler line fittings and fuel injection spider assemblies.
Fuel Systems: A primary seal for fuel pressure transducers and tank sump drain valves.
Ground Support Equipment: Used in fuel testing kits and portable refueling stations.
Technical Applications & Safety
The MS29512-04 is a "one-time use" component. Once the fitting is torqued, the O-ring deforms to fill the gaps in the metal boss.
Safety Warning: Material Mismatch Risk
Do not use in Skydrol systems. While Nitrile is excellent for fuel, it will rapidly disintegrate (liquefy) if exposed to phosphate-ester hydraulic fluids (Skydrol). For Skydrol systems, use MS28778 or AS3209 series O-rings made of Ethylene Propylene. Conversely, do not use Fluorocarbon (Viton) O-rings in low-temperature fuel applications unless specified, as they may "glassify" and leak at extremely cold temperatures.
Installation & Maintenance Addendum
Gasket Inspection: Before installation, check for "parting line" flashes or tiny nicks. Even a microscopic flaw can allow high-pressure fuel to weep past the seal.
Lubrication: Lightly coat the O-ring with clean engine oil or a specialized fuel-system lubricant (like EZ-Turn) to prevent the O-ring from "bunching" or tearing as the fitting is screwed into the boss.
Shelf Life: Nitrile has a limited shelf life (typically 15 years from the cure date). Always check the "Cure Date" on the sealed packaging to ensure the material has not begun to oxidize or turn brittle.
NOTES
MATERIAL COMPOSITION NITRILE 120 MONTH S/L PER LYCOMING 280A
Applicable Aircraft 1900 Airliner
- 1900C Airliner
- 1900D Airliner
- Beechjet 400/400A
- Bonanza 36
- Caravan or Grand Caravan EX
- Citation CJ1 or CJ1+
- Citation CJ2 or CJ2+
- Citation CJ3 or CJ3+
- Citation CJ4
- Citation Latitude
- Citation Longitude
- Citation M2
- Citation Mustang
- Citation Sovereign or Sovereign+
- Citation X
- Citation X+
- Citation XLS, XLS+ or XLS Gen2
- King Air 100
- King Air 350 or 350C FM-1 to FM-35
- King Air 360, 350i or 350C FM-36 & on
- King Air B200, B200T, B200C or B200CT
- King Air B200GT or B200CGT
- King Air C90, C90A, C90GT or E90
- King Air C90GTi Series
- Premier Model 390
- SkyCourier
List not comprehensive, may be applicable on other models.