NAS620 — Wide/Oversize Flat Washer Specification
NAS620 is a National Aerospace Standard covering flat washers with a larger outside diameter than the general-purpose NAS1149 series. It is used primarily to bridge oversized clearance holes and mount components in areas near bends, radii, or other structural interferences where a wider bearing surface is needed.
At a Glance
Key identifiers for specifying NAS620 hardware.
Overview
What the standard controls and where it's typically applied.
NAS620 defines flat washers intended primarily for mounting components in areas of bend radii and other structural interferences, where a wider outside diameter is needed to properly seat a fastener head or nut without a standard-width NAS1149 washer bridging into an unsupported area. Like other NAS drawings, it is published by the Aerospace Industries Association (AIA) and its use is entirely voluntary — AIA does not qualify suppliers or certify conformance of parts produced to it.
The standard specifies acceptable base materials and their finishes: carbon steel (cadmium plated), corrosion resistant steel (passivated per AMS2700 Method 1, Type 6 or 7, Class 1), 5052 aluminum alloy sheet per AMS-QQ-A-250/8 in H32 or H34 temper, and brass. Referenced documents are applied at the issue in effect on the date of manufacture, though existing certified material inventory may be used until depleted.
- Larger OD-to-ID ratio than NAS1149 for the same nominal bolt size.
- Part numbers use a dash-number size code, with an "L" suffix commonly denoting a large-OD variant and an "A" prefix or similar letter code identifying material.
- Certain material/finish washers are dyed a distinguishing color for visual identification, applied so it will not rub off during normal handling.
Part Number Reference
NAS620 designations combine the base number, a material/style prefix, a dash size code, and an optional finish/length suffix.
Approved Materials & Finishes
| Material | Prefix Code | Finish | Governing Spec |
|---|---|---|---|
| Carbon Steel | (none) | Cadmium Plate | QQ-P-416 |
| Corrosion Resistant Steel | C | Passivate | AMS2700, Method 1, Type 6/7, Class 1 |
| Aluminum Alloy 5052 | DD | Chemical Treatment | AMS-QQ-A-250/8, Temper H32/H34 |
| Brass | BN | None | ASTM B36 / ASTM B121 |
NAS620 is a companion, wide-OD counterpart to NAS1149. Designers should confirm which series a drawing calls out — NAS620's larger outside diameter is intended specifically for bend-radius and interference-clearance mounting, not as a general substitute for NAS1149.
Manufacturing & Quality Notes
Referenced material and finish specifications apply at the issue in effect on the date of manufacture; existing certified inventory may still be used until depleted.
This standard takes precedence over any conflicting requirement in the documents it references.
Certain washers are color-dyed for material identification; the dye must resist rubbing or smearing from normal handling and service.
As with all AIA/NAS documents, use is voluntary and AIA does not certify supplier conformance — quality assurance is the manufacturer's responsibility.
NAS620 — Frequently Asked Questions
What's the difference between NAS620 and NAS1149?
Both are National Aerospace Standard flat washers, but NAS620 has a larger outside diameter for a given bolt size. It's used where a wider bearing surface is needed, such as near bend radii or other structural interferences, while NAS1149 is the general-purpose flat washer.
What materials are available under NAS620?
Carbon steel (cadmium plated), corrosion resistant steel (passivated), 5052 aluminum alloy, and brass, each identified by a material prefix code in the part number.
What does the "L" suffix mean on a NAS620 part number?
An "L" suffix commonly denotes a large-outside-diameter variant within the NAS620 series; always confirm against the current drawing sheet for the exact size in question.
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