MS21266-4N – Aerospace Non-Metallic Edging (Nylon Grommet)
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The MS21266-4N is a high-performance, flexible aerospace edging—commonly referred to as "caterpillar grommet"—designed to protect electrical wire harnesses, hydraulic lines, and control cables from the sharp edges of airframe bulkheads and structural cutouts. Manufactured to the MIL-DTL-21266 (formerly MS21266) military standard, this non-metallic edging is an essential component for preventing chafing, which is a leading cause of electrical shorts and fluid line failures in turbine and piston aircraft.
The "4N" designation specifies the material and size: "4" denotes the width compatibility for sheet metal thicknesses ranging from 0.033 to 0.047 inches, and "N" identifies the material as Nylon 6/6. This 12.62-inch strip features a serrated, "toothed" geometry that allows it to conform to tight radii and irregular apertures (circles, ovals, or squares) without kinking or lifting, providing a continuous protective barrier between the airframe and critical systems.
Key Features
Serrated "Caterpillar" Design: The notched profile allows the edging to bend around internal and external curves of bulkheads, lightening holes, and ribs with ease.
Nylon 6/6 Construction: Provides high mechanical strength, excellent abrasion resistance, and a broad operating temperature range (-40°C to +121°C).
Self-Extinguishing Properties: Manufactured from flame-retardant materials that meet the stringent flammability requirements of the aerospace industry (UL 94V-2 or better).
Chemical Resilience: Resistant to common aviation fluids, including hydraulic oils (Skydrol), lubricating oils, and various solvents.
Positive Interference Fit: Designed to snap securely onto the edge of the sheet metal, maintaining its position under high-vibration conditions without the immediate need for secondary adhesives.
Technical Specifications
Part Number: MS21266-4N
Military Specification: MIL-DTL-21266
Material: Nylon 6/6 (Natural/Off-White)
Sheet Metal Thickness Range: 0.033" to 0.047" (0.84 mm to 1.19 mm)
Overall Length: 12.62 Inches (320.5 mm)
Width: 0.165" (Approx. Nominal)
Height: 0.160" (Approx. Nominal)
Operating Temperature: -40°F to +250°F (-40°C to +121°C)
Flammability: Meets FAR 25.853 requirements for cabin interiors.
Aircraft Compatibility
General Aviation (GA): A staple in Cessna, Piper, and Beechcraft airframes for wing ribs and firewall pass-throughs.
Business & Commercial Jets: Used in Gulfstream, Bombardier, and Boeing equipment bays to protect high-density wiring looms.
Experimental Aircraft: Popular with RV-series and Kitfox builders for finishing lightening holes and preventing wire rub in the fuselage.
Note: Check the MS21266 size chart to ensure the -4 width matches your specific bulkhead thickness.
Applications
The MS21266-4N is utilized for System Abrasion Prevention. Its primary roles include:
Lightening Hole Lining: Protecting wiring as it passes through structural holes in wing spars or fuselage frames.
Equipment Rack Protection: Edging the sharp corners of avionics trays and instrument panels.
Control Cable Routing: Providing a smooth surface for secondary control cables or vent lines that may vibrate against the airframe.
Why Choose MS21266-4N?
Choosing a genuine MIL-SPEC MS21266-4N ensures that the nylon has the correct Shore Hardness to resist cutting from sharp metal edges. Commercial "nylon trim" often uses inferior polymers that become brittle and crack when exposed to the dry, cold air at high altitudes. The MS21266 series is engineered to maintain its ductility, ensuring the "teeth" of the grommet do not snap off during the high-vibration environment of a running engine.
The MS21266-4N operates as a Mechanical Buffer governed by the physics of Friction Management. In an airframe, vibration causes relative motion between a "fixed" harness and the structure. This creates a frictional interface that can saw through insulation. The Nylon 6/6 used in the -4N has a low Coefficient of Friction, allowing the wire or line to slide against the grommet rather than being cut by the metal. Because it is a Non-Metallic component, it provides a secondary layer of dielectric isolation, ensuring that even if a wire's insulation is slightly compromised, it cannot ground against the aluminum airframe through the grommet.
Note: This is a safety-critical maintenance item. Prior to installation, deburr the metal edge to prevent cutting the nylon. For long-term security in high-vibration or high-airflow areas, a small dab of RTV or approved adhesive at the ends of the strip is recommended to prevent "migration." Installation should be performed by a certified A&P/AME in accordance with FAA AC 43.13-1B, Chapter 11.
Documentation
Acceptable Aircraft Models
- DC9
- 737-900
- 767-200ERSF
- 402NG
- 767-200
- B200CT
- MD11
- 767-300EREM
- CRJ-705
- ERJ-190-100 LR
- 737-900ER
- 800XPi
- ERJ-190-200
- MD80
- 767-300BCF
- 757-200
- C90GT
- CRJ-900
- CRJ-702
- 757-200PF
- 737-7
- 1900C
- ERJ-190-100 ECJ
- CRJ-100
- 402QPF
- 767-200EREM
- 767-300ER
- B200C
- CRJ-700ER
- DC10
- CRJ-701ER
- 767-300
- 737 MAX 8
- CRJ-900ER
- 737-8
- ERJ-170-200
- 737-9
- ERJ-170-100 SE
- ERJ-190-200 IGW
- ERJ-170-200 SU
- ERJ-190-100 IGW
- 737-700
- C90GTi
- ERJ-170-200 IGW
- 767-200ER
- MD90
- C90GTx
- B200
- 402F
- 767-200SF
- ERJ-190-200 LR
- Q400
- BBJ 737-800
- ERJ-190-100
- ERJ-170-100 SU
- MD11
- 737-800
- CRJ-440
- C90SE
- 350C
- CRJ-200
- ERJ-170-200 LL
- CRJ-702ER
- 737-10
- B200T
- 737MAX
- CRJ-700
- 737-8200
- CRJ-701
- B200GT
- 757
- 350I
- 717-200
- 737 MAX 9
- Q402F
- C90B
- C90-1
- ERJ-170-100 LR
- DC9
- C90A
- C90
- 767-400ER
- DC10
- MD80
- CRJ-900LR
- 1900
- ERJ-170-200 LR
- BBJ 737-700
- 747-400
- 767-200ERT
- 850XP
- B200CGT
- ERJ-170-100
- MD90
- 900XP
- 402Q
- 767
- 737NG
- 800XP
- E90
- 767-200EM