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Technical Data Sheet
PartsTable / COMPONENT / 4020520
4020520 ✓ 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

NUT,SELF-LOCKING,EXTENDED WASHER. Key specifications include material: IRON ALLOY 660 OVERALL, nut_style: HEXAGON, thread_class: 3B, thread_series: UNIFIED NATIONAL JOINT FINE (UNJF), overall_height: 0.391 INCHES MINIMUM AND 0.421 INCHES MAXIMUM IN, locking_feature: PREVAILING TORQUE ALL METAL DESIGN. This product is currently in active production with full OEM support.

This part is cataloged in the Federal Logistics Information System (FLIS) under NSN 5310-00-395-7841, 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
4020520
NSN: 5310-00-395-7841
FSC: 5310
CAGE: 77445 — RTX CORPORATION DBA PRATT & WHITNEY DIV PRATT &WHITNEY (USA)
SPECIFICATIONS
materialIRON ALLOY 660 OVERALL
nut_styleHEXAGON
thread_class3B
thread_seriesUNIFIED NATIONAL JOINT FINE (UNJF)
overall_height0.391 INCHES MINIMUM AND 0.421 INCHES MAXIMUM IN
locking_featurePREVAILING TORQUE ALL METAL DESIGN
special_featuresUPPER HEXAGON CASTELLATED 6 PLACES CENTER TO CENTER ALONG FLATS,0.125 IN. MIN 0.155 IN. MAX THROUGH W,0.187 IN. DEPTH IN
thread_directionRIGHT-HAND
washer_thickness0.070 INCHES NOMINAL IN
countersink_angle85.0 DEGREES MINIMUM AND 95.0 DEGREES MAXIMUM NUT
width_across_flats0.430 INCHES MINIMUM AND 0.440 INCHES MAXIMUM IN
nominal_thread_size0.375 INCHES IN
NSN5310-00-395-7841
COMPONENT DIAGRAM
NUT & WASHER — GRADE MATCHING REQUIRED Hex NUT CROSS-SECTION WASHER OD: — SIZE: — MATERIAL: — PN: 4020520 · 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
•
THREAD DIRECTION: RIGHT-HAND
•
COUNTERSINK ANGLE: 85.0 DEGREES MINIMUM AND 95.0 DEGREES MAXIMUM NUT
•
THREAD SERIES: UNIFIED NATIONAL JOINT FINE (UNJF)
•
NOMINAL THREAD SIZE: 0.375 INCHES IN
•
THREAD QUANTITY PER INCH: 24
•
MATERIAL: IRON ALLOY 660 OVERALL
TECHNICAL CHARACTERISTICS (FLIS)
SPECIAL FEATURESUPPER HEXAGON CASTELLATED 6 PLACES CENTER TO CENTER ALONG FLATS,0.125 IN. MIN 0.155 IN. MAX THROUGH W,0.187 IN. DEPTH IN
THREAD DIRECTIONRIGHT-HAND
OVERALL HEIGHT0.391 INCHES MINIMUM AND 0.421 INCHES MAXIMUM IN
COUNTERSINK ANGLE85.0 DEGREES MINIMUM AND 95.0 DEGREES MAXIMUM NUT
THREAD SERIESUNIFIED NATIONAL JOINT FINE (UNJF)
NOMINAL THREAD SIZE0.375 INCHES IN
THREAD QUANTITY PER INCH24
MATERIALIRON ALLOY 660 OVERALL
MATERIAL DOCUMENT AND CLASSIFICATIONAMS 5737 ASSN STD SINGLE MATERIAL RESPONSE OVERALL
WIDTH ACROSS FLATS0.430 INCHES MINIMUM AND 0.440 INCHES MAXIMUM IN
VERIFIED SUBSTITUTES & CROSS-REFERENCES 8
4010085001Interchangeable
interchangeable cross-reference
interchangeable
E4033Interchangeable
interchangeable cross-reference
interchangeable
4010085Interchangeable
interchangeable cross-reference
interchangeable
2187417Interchangeable
interchangeable cross-reference
interchangeable
ST2495-12Interchangeable
interchangeable cross-reference
interchangeable
E10787-6Interchangeable
Same NIIN cross-reference
interchangeable
LIFECYCLE
StatusACTIVE
AvailabilityOEM and secondary market
RoHS CompliantEAR99Not HAZMAT
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FREQUENTLY ASKED QUESTIONS
What is 4020520?
4020520 is a NUT,SELF-LOCKING,EXTENDED WASHER.
What parts can replace 4020520?
There are 8 known substitutes for 4020520: 4010085001, E4033, 4010085 and 5 more. Substitute compatibility should be verified for your specific system.
What is the NSN for 4020520?
4020520 is cataloged in the Federal Logistics Information System (FLIS) under NSN 5310-00-395-7841. 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