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K39781-4 — WASHER,CONCAVE

✓ Government record, cited
— · NUT WASHER
PRODUCT OVERVIEW

K39781-4: WASHER,CONCAVE.

The WASHER,CONCAVE is a the manufacturer industrial component. Key specifications include radius: 0.290 INCHES MINIMUM AND 0.310 INCHES MAXIMUM IN, material: STEEL COMP 8740 OVERALL, recess_depth: 0.025 INCHES NOMINAL IN, hole_diameter: 0.260 INCHES MINIMUM AND 0.270 INCHES MAXIMUM IN, surface_finish: 32.0 MICROINCHES ALL SURFACES, hardness_rating: 40.0 ROCKWELL C MINIMUM AND 46.0 ROCKWELL C MAXIMUM. This part is cataloged in the U.S.

Government catalog under NSN 5310-01-360-2208, 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
K39781-4
NSN: 5310-01-360-2208
NIINs: 013602208, 016588336
FSC: 5310 — Nuts and Washers
CAGE: 15653 — HOWMET GLOBAL FASTENING SYSTEMS INC (USA)
SPECIFICATIONS
radius0.290 INCHES MINIMUM AND 0.310 INCHES MAXIMUM IN
materialSTEEL COMP 8740 OVERALL
recess_depth0.025 INCHES NOMINAL IN
hole_diameter0.260 INCHES MINIMUM AND 0.270 INCHES MAXIMUM IN
surface_finish32.0 MICROINCHES ALL SURFACES
hardness_rating40.0 ROCKWELL C MINIMUM AND 46.0 ROCKWELL C MAXIMUM
outside_diameter0.454 INCHES MINIMUM AND 0.464 INCHES MAXIMUM IN
special_featuresSPHERICAL RADIUS 0.290 IN. MIN 0.310 IN. MA,COUNTERSINK DIA 0.332 IN. MIN 0.342 IN. MAX,COUNTERSINK DEPTH 0.025 IN.,RECESS ANGLE 89 DEG MIN 91 DEG MAX IN
style_designatorCONCAVE
surface_treatmentCADMIUM AND CHROMATE OVERALL
material_thickness0.075 INCHES MINIMUM AND 0.100 INCHES MAXIMUM IN
end_item_identificationB1-BACFT
NSN5310-01-360-2208
COMPONENT DIAGRAM
NUT & WASHER — GRADE MATCHING REQUIRED Hex NUT CROSS-SECTION WASHER OD: — SIZE: — MATERIAL: — PN: K39781-4 · 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
•
SURFACE FINISH: 32.0 MICROINCHES ALL SURFACES
•
SURFACE TREATMENT DOCUMENT AND CLASSIFICATION: QQ-P-416,TY 2,CL 3 FED SPEC SINGLE TREATMENT RESPONSE OVERALL
•
HARDNESS RATING: 40.0 ROCKWELL C MINIMUM AND 46.0 ROCKWELL C MAXIMUM
•
STYLE DESIGNATOR: CONVEX
•
MATERIAL DOCUMENT AND CLASSIFICATION: MIL-S-6049 MIL SPEC 1ST MATERIAL RESPONSE OR MIL-S-6758 MIL SPEC 2ND MATERIAL RESPONSE OR MIL-S-18729 MIL SPEC 2ND MATERIAL RESPONSE OVERALL
•
OUTSIDE DIAMETER: 0.454 INCHES MINIMUM AND 0.464 INCHES MAXIMUM IN
•
MATERIAL THICKNESS: 0.075 INCHES MINIMUM AND 0.095 INCHES MAXIMUM IN
TECHNICAL CHARACTERISTICS
SURFACE FINISH32.0 MICROINCHES ALL SURFACES
SURFACE TREATMENT DOCUMENT AND CLASSIFICATIONQQ-P-416,TY 2,CL 3 FED SPEC SINGLE TREATMENT RESPONSE OVERALL
HARDNESS RATING40.0 ROCKWELL C MINIMUM AND 46.0 ROCKWELL C MAXIMUM
STYLE DESIGNATORCONVEX
MATERIAL DOCUMENT AND CLASSIFICATIONMIL-S-6049 MIL SPEC 1ST MATERIAL RESPONSE OR MIL-S-6758 MIL SPEC 2ND MATERIAL RESPONSE OR MIL-S-18729 MIL SPEC 2ND MATERIAL RESPONSE OVERALL
OUTSIDE DIAMETER0.454 INCHES MINIMUM AND 0.464 INCHES MAXIMUM IN
MATERIAL THICKNESS0.075 INCHES MINIMUM AND 0.095 INCHES MAXIMUM IN
SPECIAL FEATURESSPHERICAL RADIUS 0.290 IN. MIN 0.310 IN. MA,COUNTERSINK DIA 0.332 IN. MIN 0.342 IN. MAX,COUNTERSINK DEPTH 0.025 IN.,RECESS ANGLE 89 DEG MIN 91 DEG MAX IN
SURFACE TREATMENTCADMIUM AND CHROMATE OVERALL
MATERIALSTEEL COMP 8740 OR STEEL COMP 4130 OVERALL
SUBSTITUTES & CROSS-REFERENCES 2
MIL-W-45595/6Reference document
Same NSN cross-reference
Reference document — Identification reference
M45595/6-02Same NSN cross-reference
Same NSN cross-reference
Also cataloged under this NSN
LIFECYCLE
NSN statusCancelled· U.S. Government catalog
Acquisition advice: Terminal item — no further procurement; issued until stock is exhaustedNo demilitarization required
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FREQUENTLY ASKED QUESTIONS
What is K39781-4?
K39781-4 is a WASHER,CONCAVE.
What parts can replace K39781-4?
There are 2 known substitutes for K39781-4: MIL-W-45595/6, M45595/6-02. Substitute compatibility should be verified for your specific system.
What is the NSN for K39781-4?
K39781-4 is cataloged in the U.S. Government catalog under NSN 5310-01-360-2208. This indicates validated use in U.S. government and defense supply chains.
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✓ PartsTable — the parts reference. Every fact cited to its source.
PartsTable Design LLC · partstable.com
U.S. Government catalog: edition PUBLOGDVD v12.0.0 (OCT 2026), edition date 2026-10-01, retrieved 2026-10-18.
PartsTable commercial catalog: edition Unified commercial catalog snapshot through 2026-09-28, edition date not on file, retrieved 2026-09-28.