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21FKF-518 — NUT,SELF-LOCKING,HEXAGON

✓ Government record, cited
— · NUT WASHER
PRODUCT OVERVIEW

21FKF-518: NUT,SELF-LOCKING,HEXAGON.

The NUT,SELF-LOCKING,HEXAGON is a the manufacturer industrial component. Key specifications include material: STEEL OVERALL, nut_style: HEXAGON, nut_height: 0.353 INCHES NOMINAL IN, thread_class: 2B, thread_series: UNIFIED NATIONAL COARSE (UNC), locking_feature: PREVAILING TORQUE ALL METAL DESIGN. This part is cataloged in the U.S.

Government catalog under NSN 5310-01-148-3697, 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
21FKF-518
NSN: 5310-01-148-3697
FSC: 5310 — Nuts and Washers
CAGE: 56878 — SPS TECHNOLOGIES, LLC DBA PB FASTENERS (USA)
SPECIFICATIONS
materialSTEEL OVERALL
nut_styleHEXAGON
nut_height0.353 INCHES NOMINAL IN
thread_class2B
thread_seriesUNIFIED NATIONAL COARSE (UNC)
locking_featurePREVAILING TORQUE ALL METAL DESIGN
thread_directionRIGHT-HAND
surface_treatmentCADMIUM OVERALL
width_across_flats0.492 INCHES MINIMUM AND 0.502 INCHES MAXIMUM IN
nominal_thread_size0.312 INCHES IN
bearing_surface_typeCHAMFERED
thread_quantity_per_inch18
NSN5310-01-148-3697
COMPONENT DIAGRAM
NUT & WASHER — GRADE MATCHING REQUIRED Hex NUT CROSS-SECTION WASHER OD: — SIZE: — MATERIAL: — PN: 21FKF-518 · 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: 0.492 INCHES MINIMUM AND 0.502 INCHES MAXIMUM IN
•
THREAD SERIES: UNIFIED NATIONAL COARSE (UNC)
•
THREAD DIRECTION: RIGHT-HAND
•
NOMINAL THREAD SIZE: 0.312 INCHES IN
•
LOCKING FEATURE: PREVAILING TORQUE ALL METAL DESIGN
•
NUT HEIGHT: 0.353 INCHES NOMINAL IN
•
SURFACE TREATMENT: CADMIUM OVERALL
•
NUT STYLE: HEXAGON
TECHNICAL CHARACTERISTICS
WIDTH ACROSS FLATS0.492 INCHES MINIMUM AND 0.502 INCHES MAXIMUM IN
THREAD SERIESUNIFIED NATIONAL COARSE (UNC)
THREAD DIRECTIONRIGHT-HAND
NOMINAL THREAD SIZE0.312 INCHES IN
LOCKING FEATUREPREVAILING TORQUE ALL METAL DESIGN
NUT HEIGHT0.353 INCHES NOMINAL IN
SURFACE TREATMENTCADMIUM OVERALL
NUT STYLEHEXAGON
THREAD CLASS2B
THREAD QUANTITY PER INCH18
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

No substitute or cross-reference records for this part.

LIFECYCLE
NSN statusActive· U.S. Government catalog
No demilitarization required
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FREQUENTLY ASKED QUESTIONS
What is 21FKF-518?
21FKF-518 is a NUT,SELF-LOCKING,HEXAGON.
What is the NSN for 21FKF-518?
21FKF-518 is cataloged in the U.S. Government catalog under NSN 5310-01-148-3697. 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.