A-A-55217C is a U.S. Government Commercial Item Description covering meta-aramid spun staple sewing thread used in flame-resistant protective clothing and flight safety equipment. This guide outlines the core requirements engineers and procurement teams typically review, including type classification, Tex-based strength and elongation ranges, heat aging performance, finishes, labeling, and workmanship.
A-A-55217C is a U.S. Government Commercial Item Description (CID) for thread, meta-aramid, spun staple used to sew flame-resistant protective combat clothing and flight safety equipment. This page summarizes the key requirements engineers and procurement teams typically need when specifying Nomex® meta-aramid spun thread.
Rocket-Fibers supplies Nomex® Spun Sewing Threads manufactured to meet A-A-55217C Type I requirements for demanding FR sewing applications.
What The Specification Covers
A-A-55217C covers a spun staple meta-aramid thread intended for sewing FR uniforms and safety equipment. The CID defines thread construction and performance requirements and specifies test methods for verification.
Type Classification
- Type I — Normal Performance
- Type II — Deleted from the specification
The CID also specifies that the thread yarn is made using 1.5 to 2.0 denier per filament meta-aramid fiber, and unless otherwise stated, the final twist direction is Z.
What Are Spun Sewing Threads?
Spun sewing threads are produced from short staple fibers rather than continuous filament yarns. Staple fibers are processed and twisted into plies, then twisted into the finished thread for consistent sewability and durability in textile assemblies.
This construction gives spun thread a softer hand and good sewing performance for protective garments and safety products, while still maintaining the flame resistance and thermal stability associated with meta-aramid fiber.
A-A-55217C Tex Table (Type I)
A-A-55217C specifies physical characteristics for Type I thread by Tex range, including ply construction, minimum breaking strength, and maximum elongation.
| Tex Range | Ply | Breaking Strength (lbf), Minimum | Elongation (%), Maximum |
|---|---|---|---|
| 24–27 | 2 | 1.3 | 32 |
| 35–40 | 3 | 2.0 | 32 |
| 50–60 | 3 | 3.0 | 35 |
| 70–80 | 4 | 4.5 | 38 |
| 90–100 | 4 | 5.5 | 38 |
Note: Tex size is based on thread weight in grams per 1,000 meters.
Thermal And Flame Properties Of Nomex® Sewing Thread
Meta-aramid fibers such as Nomex® are primarily selected for their excellent thermal stability and inherent flame resistance. Unlike conventional synthetic sewing threads, Nomex® does not melt or drip when exposed to high heat, which is a critical advantage in protective apparel and flight safety applications.
These fibers are engineered to maintain integrity in elevated temperature environments and are widely used where short-term flame exposure, flash fire resistance, or long-term heat aging performance are important design requirements.
Compared with conventional sewing threads, Nomex® spun thread offers:
- Inherent flame resistance
- Non-melting behavior under heat exposure
- Excellent thermal stability
- Reliable performance in FR sewn assemblies
- Durability in protective clothing applications
While meta-aramid threads are not intended to match para-aramid sewing threads in tensile strength, they are preferred in many flame-resistant garments and heat-protective systems because thermal performance is the primary requirement.
Heat Aging Requirement
A-A-55217C includes a heat aging requirement in which specimens are exposed for 20 minutes at 550°F (±10°F) in an air-circulating oven, then conditioned and tested for breaking strength.
After aging, the minimum breaking strength must remain at 85% of the initial breaking strength. This requirement helps ensure the thread maintains performance after short-term exposure to elevated temperatures.
Finishes And Sewing Lubricants
The CID allows only the types of finishes commonly used on commercial sewing threads, such as minimal lubricants to facilitate sewing.
- No finish may be applied to increase breaking strength.
- No finish may be used that diminishes flame resistance.
- Applied finishes must support sewability without compromising specification performance.
Color And Colorfastness
Color is specified by the end item specification or contract. A-A-55217C also includes colorfastness requirements for laundering and defines evaluation procedures for shade matching.
This is especially important for military, flight safety, and protective clothing programs where consistent appearance and durability after laundering are required.
Put-Up And Labeling
Unless otherwise specified, the thread may be put up on commercial spools, cones, tubes, or bobbins. The thread should be wound in one continuous length with layers free of entanglement, and the outside end secured to prevent unwinding during handling, shipping, or storage.
Each holder label should include information such as:
- Length in yards
- Direction of twist or cone weight
- Color
- Tex size
- Manufacturer name
- Nomenclature specifying type and construction
Workmanship Requirements
A-A-55217C includes workmanship limits for knots and splices and defines visual examination defects and acceptance criteria as specified in the contract or purchase order.
These workmanship requirements help ensure consistent sewability, uniform appearance, and dependable performance in finished FR sewn assemblies.
Nomex® Spun Thread Supply
Rocket-Fibers supplies Nomex® Spun Sewing Threads for FR sewing applications requiring dependable heat and flame performance. If you need a specific Tex size, color, or put-up format, contact us with your A-A-55217C ordering requirements.
