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KFN556-3 — NUT,SELF-LOCKING,EXTENDED WASHER

✓ Government record, cited
— · NUT WASHER
PRODUCT OVERVIEW

KFN556-3: NUT,SELF-LOCKING,EXTENDED WASHER.

NUT,SELF-LOCKING,EXTENDED WASHER. Key specifications include material: STEEL COMP 8740 OR STEEL COMP E4340 NUT, nut_style: HEXAGON, thread_class: 3B, thread_series: UNIFIED NATIONAL JOINT FINE (UNJF), overall_height: 0.301 INCHES MAXIMUM IN, hardness_rating: 39.0 ROCKWELL C MINIMUM AND 43.0 ROCKWELL C MAXIMUM. This part is cataloged in the U.S.

Government catalog under NSN 5310-01-223-6531, 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
KFN556-3
NSN: 5310-01-223-6531
FSC: 5310 — Nuts and Washers
CAGE: 92215 — HOWMET GLOBAL FASTENING SYSTEMS INC DIV TORRANCE OPERATIONS (USA)
SPECIFICATIONS
materialSTEEL COMP 8740 OR STEEL COMP E4340 NUT
nut_styleHEXAGON
thread_class3B
thread_seriesUNIFIED NATIONAL JOINT FINE (UNJF)
overall_height0.301 INCHES MAXIMUM IN
hardness_rating39.0 ROCKWELL C MINIMUM AND 43.0 ROCKWELL C MAXIMUM
locking_featurePREVAILING TORQUE ALL METAL DESIGN
special_featuresCETYL ALCOHOL LUBRICANT PER MIL-L-87132,TY 1,GRADE A
thread_directionRIGHT-HAND
washer_thickness0.088 INCHES MINIMUM AND 0.092 INCHES MAXIMUM IN
surface_treatmentCADMIUM AND CHROMATE NUT
width_across_flats0.243 INCHES MINIMUM AND 0.251 INCHES MAXIMUM IN
NSN5310-01-223-6531
COMPONENT DIAGRAM
NUT & WASHER — GRADE MATCHING REQUIRED Hex NUT CROSS-SECTION WASHER OD: — SIZE: — MATERIAL: — PN: KFN556-3 · 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
•
WASHER OUTSIDE DIAMETER: 0.348 INCHES MAXIMUM IN
•
WIDTH ACROSS FLATS: 0.243 INCHES MINIMUM AND 0.251 INCHES MAXIMUM IN
•
SURFACE TREATMENT DOCUMENT AND CLASSIFICATION: QQ-P-416,TY 2,CL 2 FED SPEC SINGLE TREATMENT RESPONSE NUT
•
THREAD SERIES: UNIFIED NATIONAL JOINT FINE (UNJF)
•
HARDNESS RATING: 39.0 ROCKWELL C MINIMUM AND 43.0 ROCKWELL C MAXIMUM
•
WASHER THICKNESS: 0.088 INCHES MINIMUM AND 0.092 INCHES MAXIMUM IN
•
MATERIAL DOCUMENT AND CLASSIFICATION: MIL-P-19468 MIL SPEC SINGLE MATERIAL RESPONSE WASHER
TECHNICAL CHARACTERISTICS
OVERALL HEIGHT0.301 INCHES MAXIMUM IN
WASHER OUTSIDE DIAMETER0.348 INCHES MAXIMUM IN
WIDTH ACROSS FLATS0.243 INCHES MINIMUM AND 0.251 INCHES MAXIMUM IN
SURFACE TREATMENT DOCUMENT AND CLASSIFICATIONQQ-P-416,TY 2,CL 2 FED SPEC SINGLE TREATMENT RESPONSE NUT
THREAD SERIESUNIFIED NATIONAL JOINT FINE (UNJF)
HARDNESS RATING39.0 ROCKWELL C MINIMUM AND 43.0 ROCKWELL C MAXIMUM
WASHER THICKNESS0.088 INCHES MINIMUM AND 0.092 INCHES MAXIMUM IN
MATERIAL DOCUMENT AND CLASSIFICATIONMIL-P-19468 MIL SPEC SINGLE MATERIAL RESPONSE WASHER
MATERIAL DOCUMENT AND CLASSIFICATIONMIL-S-6049 MIL SPEC 1ST MATERIAL RESPONSE OR MIL-S-5000 MIL SPEC 2ND MATERIAL RESPONSE NUT
THREAD DIRECTIONRIGHT-HAND
OTHER ITEMS IN FSC 5310 — Nuts and Washers
Items in the same Federal Supply class. No interchangeability or substitution relationship is implied.
5310-00-000-0040 5310-00-000-0077 5310-00-000-0079 5310-00-000-1146 5310-00-000-3815 5310-00-000-4532 5310-00-000-4540
SUBSTITUTES & CROSS-REFERENCES 1
BH00529-3Reference document
Same NSN cross-reference
Reference document — Secondary reference
LIFECYCLE
NSN statusActive· U.S. Government catalog
Acquisition advice: Insurance item — stocked against contingency demandNo demilitarization required
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FREQUENTLY ASKED QUESTIONS
What is KFN556-3?
KFN556-3 is a NUT,SELF-LOCKING,EXTENDED WASHER.
What parts can replace KFN556-3?
There is 1 known substitute for KFN556-3: BH00529-3. Substitute compatibility should be verified for your specific system.
What is the NSN for KFN556-3?
KFN556-3 is cataloged in the U.S. Government catalog under NSN 5310-01-223-6531. 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.
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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.