Military Washers — Flat, Lock & Countersunk
Military washers distribute fastener clamp load, protect joined surfaces, prevent loosening, and take up dimensional stack-up — every seemingly simple disc governed by tight tolerances on outside diameter, hole size, thickness, and bearing surface finish.
Washer Configurations We Manufacture
Function determines geometry: distributing load, locking against rotation, or seating a countersunk fastener flush.
Flat Washers
Distribute a bolt or nut's clamping load across a wider bearing area, protect the joined surface, and take up small gaps in a fastener stack-up.
Lock Washers
Spring (helical) or tooth-style washers that add spring tension or mechanical bite to resist a joint loosening under vibration.
Countersunk Washers
Angled bearing surface matches a countersunk fastener head, allowing a flush-mount screw to seat properly against an otherwise flat panel.
Overview
NAS1149 is the modern backbone of the aerospace flat washer family, developed as a direct, size-for-size replacement for the legacy AN960 series, while NAS620 provides a wider-OD companion for bend-radius and interference-clearance mounting where NAS1149's standard outside diameter doesn't provide enough bearing surface.
Lock washers split into two distinct mechanisms: spring (helical) lock washers under FF-W-84 rely on axial spring tension across several material classes (carbon steel through K-Monel), while tooth lock washers under FF-W-100 rely on sharp, twisted teeth that physically bite into both mating surfaces — a configuration also favored for electrical grounding connections since the teeth cut through surface oxide to establish a reliable bond.
- FF-W-92 covers plain flat washers with specific rules on hole-to-OD ratio (≤75%), minimum thickness, and bearing surface finish (better than 32 microinches).
- Washer material is typically matched to the mating bolt or the joint's corrosion environment: steel for general strength, CRES or titanium for corrosion/weight-critical applications, aluminum for weight-critical airframe work.
Which Washer Do You Need?
Applicable Standards
Explore the individual military washer specifications Ananka manufactures to.
Military Washers — Frequently Asked Questions
Should I use NAS1149 or AN960 washers on a new design?
Specify NAS1149. It was developed as a direct substitute for AN960, which is officially superseded — AN960 part numbers are only retained for legacy drawing cross-reference and MRO support.
What's the difference between spring and tooth lock washers?
Spring (helical) lock washers resist loosening primarily through axial spring tension from their split, coiled cross-section. Tooth lock washers resist loosening through direct mechanical engagement — sharp teeth bite into both mating surfaces, which also makes them useful for electrical grounding.
When do I need a wide-OD washer instead of a standard flat washer?
NAS620 wide-OD washers are used specifically near bend radii or other structural interferences where a standard NAS1149 washer's outside diameter isn't wide enough to properly seat against the surrounding structure.
Need Military Washers to Print?
Ananka Fasteners manufactures military washers to NAS, AN, and federal specifications with full material traceability and Mill Test Certification on every lot.
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