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PartsTable / COMPONENT / 21056A
21056A ✓ 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 NUT,PLAIN,CASTELLATED,HEXAGON is a the manufacturer industrial component. Key specifications include material: STEEL COMP 3140 OR STEEL COMP 2330 OR STEEL COMP 4135 OR STEEL COMP 4140 OR STEEL COMP 4037 OVERALL, nut_style: CASTELLATED, HEXAGON, nut_height: 0.448 INCHES MINIMUM AND 0.458 INCHES MAXIMUM IN, thread_class: 3B, thread_series: UNF, thread_direction: RIGHT-HAND. This part is cataloged in the Federal Logistics Information System (FLIS) under NSN 5310-00-274-7731, 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
21056A
NSN: 5310-00-274-7731
FSC: 5310
CAGE: 1ML14 — BRINKLEY TECHNOLOGY GROUP LLC DBA HERCULES MANUFACTURING (USA)
SPECIFICATIONS
materialSTEEL COMP 3140 OR STEEL COMP 2330 OR STEEL COMP 4135 OR STEEL COMP 4140 OR STEEL COMP 4037 OVERALL
nut_styleCASTELLATED, HEXAGON
nut_height0.448 INCHES MINIMUM AND 0.458 INCHES MAXIMUM IN
thread_class3B
thread_seriesUNF
thread_directionRIGHT-HAND
width_across_flats0.612 INCHES MINIMUM AND 0.625 INCHES MAXIMUM IN
nominal_thread_size0.438 INCHES IN
bearing_surface_typeWASHER FACED
thread_quantity_per_inch20
material_document_and_classificationSAE ASSN STD 1ST MATERIAL RESPONSE OR SAE ASSN STD 2ND MATERIAL RESPONSE OR SAE ASSN STD 3RD MATERIAL RESPONSE OR SAE ASSN STD 4TH MATERIAL RESPONSE OR AISI ASSN STD 5TH MATERIAL RESPONSE OVERALL
NSN5310-00-274-7731
COMPONENT DIAGRAM
NUT & WASHER — GRADE MATCHING REQUIRED Hex NUT CROSS-SECTION WASHER OD: — SIZE: — MATERIAL: — PN: 21056A · 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
•
NUT STYLE: CASTELLATED, HEXAGON
•
WIDTH ACROSS FLATS: 0.612 INCHES MINIMUM AND 0.625 INCHES MAXIMUM IN
•
THREAD QUANTITY PER INCH: 20
•
THREAD CLASS: 3B
•
THREAD DIRECTION: RIGHT-HAND
•
NUT HEIGHT: 0.448 INCHES MINIMUM AND 0.458 INCHES MAXIMUM IN
•
BEARING SURFACE TYPE: WASHER FACED
•
MATERIAL DOCUMENT AND CLASSIFICATION: SAE ASSN STD 1ST MATERIAL RESPONSE OR SAE ASSN STD 2ND MATERIAL RESPONSE OR SAE ASSN STD 3RD MATERIAL RESPONSE OR SAE ASSN STD 4TH MATERIAL RESPONSE OR AISI ASSN STD 5TH MATERIAL RESPONSE OVERALL
TECHNICAL CHARACTERISTICS (FLIS)
NUT STYLECASTELLATED, HEXAGON
WIDTH ACROSS FLATS0.612 INCHES MINIMUM AND 0.625 INCHES MAXIMUM IN
THREAD QUANTITY PER INCH20
THREAD CLASS3B
THREAD DIRECTIONRIGHT-HAND
NUT HEIGHT0.448 INCHES MINIMUM AND 0.458 INCHES MAXIMUM IN
BEARING SURFACE TYPEWASHER FACED
MATERIAL DOCUMENT AND CLASSIFICATIONSAE ASSN STD 1ST MATERIAL RESPONSE OR SAE ASSN STD 2ND MATERIAL RESPONSE OR SAE ASSN STD 3RD MATERIAL RESPONSE OR SAE ASSN STD 4TH MATERIAL RESPONSE OR AISI ASSN STD 5TH MATERIAL RESPONSE OVERALL
MATERIALSTEEL COMP 3140 OR STEEL COMP 2330 OR STEEL COMP 4135 OR STEEL COMP 4140 OR STEEL COMP 4037 OVERALL
NOMINAL THREAD SIZE0.438 INCHES IN
VERIFIED SUBSTITUTES & CROSS-REFERENCES 21
21056Interchangeable
interchangeable cross-reference
interchangeable
57020Interchangeable
PCI-X Ultra320 Dual Channel Adapter
interchangeable
8933179-1Interchangeable
interchangeable cross-reference
interchangeable
B94.2-1971 TABLE 5Interchangeable
interchangeable cross-reference
interchangeable
20710Interchangeable
interchangeable cross-reference
interchangeable
506.3125Interchangeable
interchangeable cross-reference
interchangeable
LIFECYCLE
StatusCANCELLED
Availability—
RoHS CompliantEAR99Not HAZMAT
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FREQUENTLY ASKED QUESTIONS
What is 21056A?
21056A is a NUT,PLAIN,CASTELLATED,HEXAGON.
What parts can replace 21056A?
There are 21 known substitutes for 21056A: 21056, 57020, 8933179-1 and 18 more. Substitute compatibility should be verified for your specific system.
Is 21056A still available?
21056A is currently cancelled.
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✓ Validated with multiple authoritative sources, including Government, OEM, and Certified sources.
PartsTable Design LLC · partstable.com
Last verified: July 2026