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3-66391 ✓ Verified by PartsTable
— · NUT WASHER
WHAT YOU NEED TO KNOW
Match nut grade to bolt grade for full strength Lock nuts prevent loosening under vibration
Don't mix grades — weakens the joint
PRODUCT OVERVIEW

The WASHER,FLAT is a the manufacturer industrial component. Key specifications include material: ALUMINUM ALLOY OVERALL, thickness: 0.064 INCHES NOMINAL IN, hole_diameter: 0.260 INCHES MINIMUM AND 0.280 INCHES MAXIMUM IN, overall_diameter: 1.000 INCHES NOMINAL IN, surface_treatment: ANODIZE OVERALL, width_across_flats: 0.600 INCHES NOMINAL IN. This product is currently in active production with full OEM support.

This part is cataloged in the Federal Logistics Information System (FLIS) under NSN 5310-00-033-7112, indicating validated use in U.S. government and defense logistics supply chains. Available through authorized enterprise resellers and TPM (Third Party Maintenance) channels.

Verify compatibility with your specific system configuration before ordering.

WHERE IT FITS
3-66391
NSN: 5310-00-033-7112
FSC: 5310
CAGE: 81205 — THE BOEING COMPANY DIV DEFENSE (USA)
SPECIFICATIONS
materialALUMINUM ALLOY OVERALL
thickness0.064 INCHES NOMINAL IN
hole_diameter0.260 INCHES MINIMUM AND 0.280 INCHES MAXIMUM IN
overall_diameter1.000 INCHES NOMINAL IN
surface_treatmentANODIZE OVERALL
width_across_flats0.600 INCHES NOMINAL IN
peripheral_shape_styleROUND W/FLATS
center_hole_shape_styleROUND
cross-sectional_shape_styleRECTANGULAR
material_document_and_classificationQQ-A-287 FED SPEC SINGLE MATERIAL RESPONSE OVERALL
surface_treatment_document_and_classificationMIL-A-8625 MIL SPEC SINGLE TREATMENT RESPONSE OVERALL
NSN5310-00-033-7112
COMPONENT DIAGRAM
NUT & WASHER — GRADE MATCHING REQUIRED Hex NUT CROSS-SECTION WASHER OD: — SIZE: — MATERIAL: — PN: 3-66391 · OEM ⚠ VERIFY BEFORE ORDERING Grade matters for torque spec — don't mix grades. A Grade 5 nut on a Grade 8 bolt weakens the joint. Lock nuts, wing nuts, and castle nuts are NOT interchangeable with standard hex ✓ BROKER TIP Match nut to bolt thread class and material. Stainless bolt + zinc nut = galvanic corrosion. Always verify finish matches (plain, zinc, hot-dip galvanized) PARTSTABLE TECHNICAL DRAWING — NOT TO SCALE
KEY FEATURES
•
WIDTH ACROSS FLATS: 0.600 INCHES NOMINAL IN
•
THICKNESS: 0.064 INCHES NOMINAL IN
•
MATERIAL: ALUMINUM ALLOY OVERALL
•
OVERALL DIAMETER: 1.000 INCHES NOMINAL IN
•
CROSS-SECTIONAL SHAPE STYLE: RECTANGULAR
•
SURFACE TREATMENT: ANODIZE OVERALL
•
CENTER HOLE SHAPE STYLE: ROUND
•
SURFACE TREATMENT DOCUMENT AND CLASSIFICATION: MIL-A-8625 MIL SPEC SINGLE TREATMENT RESPONSE OVERALL
TECHNICAL CHARACTERISTICS (FLIS)
WIDTH ACROSS FLATS0.600 INCHES NOMINAL IN
THICKNESS0.064 INCHES NOMINAL IN
MATERIALALUMINUM ALLOY OVERALL
OVERALL DIAMETER1.000 INCHES NOMINAL IN
CROSS-SECTIONAL SHAPE STYLERECTANGULAR
SURFACE TREATMENTANODIZE OVERALL
CENTER HOLE SHAPE STYLEROUND
SURFACE TREATMENT DOCUMENT AND CLASSIFICATIONMIL-A-8625 MIL SPEC SINGLE TREATMENT RESPONSE OVERALL
MATERIAL DOCUMENT AND CLASSIFICATIONQQ-A-287 FED SPEC SINGLE MATERIAL RESPONSE OVERALL
PERIPHERAL SHAPE STYLEROUND W/FLATS
VERIFIED SUBSTITUTES & CROSS-REFERENCES 11
2661058B018Interchangeable
interchangeable cross-reference
interchangeable
MS29513-18Interchangeable
interchangeable cross-reference
interchangeable
MS29513-018Interchangeable
interchangeable cross-reference
interchangeable
9937B406Interchangeable
interchangeable cross-reference
interchangeable
GB520Interchangeable
interchangeable cross-reference
interchangeable
520 GBInterchangeable
interchangeable cross-reference
interchangeable
LIFECYCLE
StatusACTIVE
AvailabilityOEM and secondary market
RoHS CompliantEAR99Not HAZMAT
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FREQUENTLY ASKED QUESTIONS
What is 3-66391?
3-66391 is a WASHER,FLAT.
What parts can replace 3-66391?
There are 11 known substitutes for 3-66391: 2661058B018, MS29513-18, MS29513-018 and 8 more. Substitute compatibility should be verified for your specific system.
What is the NSN for 3-66391?
3-66391 is cataloged in the Federal Logistics Information System (FLIS) under NSN 5310-00-033-7112. This indicates validated use in U.S. government and defense supply chains.
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✓ Validated with multiple authoritative sources, including Government, OEM, and Certified sources.
PartsTable Design LLC · partstable.com
Last verified: July 2026