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PartsTable / COMPONENT / AS21921-4W
AS21921-4W ✓ Verified by PartsTable
— · HOSE FITTING
WHAT YOU NEED TO KNOW
PTFE tape on tapered threads (NPT/BSPT) JIC/AN flare connections seal metal-to-metal — no tape
NPT != BSPT — look identical, NOT interchangeable
PRODUCT OVERVIEW

The NUT,TUBE COUPLING is a the manufacturer industrial component. Key specifications include material: ALUMINUM ALLOY OVERALL, nut_style: TUBE COUPLING, nut_height: 0.72 INCHES NOMINAL IN, seat_angle: 45.0 DEGREES NOMINAL, thread_class: 3B, thread_series: UNIFIED NATIONAL JOINT FINE (UNJF). This product is currently in active production with full OEM support.

This part is cataloged in the Federal Logistics Information System (FLIS) under NSN 4730-01-667-6443, 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
AS21921-4W
NSN: 4730-01-667-6443
FSC: 4730
CAGE: 0U583 — SAE INTERNATIONAL DBA SAE INTERNATIONAL (USA)
SPECIFICATIONS
materialALUMINUM ALLOY OVERALL
nut_styleTUBE COUPLING
nut_height0.72 INCHES NOMINAL IN
seat_angle45.0 DEGREES NOMINAL
thread_class3B
thread_seriesUNIFIED NATIONAL JOINT FINE (UNJF)
thread_directionRIGHT-HAND
width_across_flats0.558 INCHES MINIMUM AND 0.565 INCHES MAXIMUM IN
nominal_thread_size0.4375 INCHES IN
end_item_identificationPSP BLK20 A K
smallest_inside_diameter0.300 INCHES MINIMUM AND 0.305 INCHES MAXIMUM IN
thread_quantity_per_inch20.0
NSN4730-01-667-6443
COMPONENT DIAGRAM
HOSE FITTING — THREAD TYPE IS CRITICAL END A: — STRAIGHT END B: — SPECIFICATIONS Thread: — Material: — Pressure: — PN: AS21921-4W · OEM ⚠ VERIFY BEFORE ORDERING NPT ≠ BSPT — tapered threads look identical but are NOT interchangeable. Wrong thread = leak. JIC (37°) ≠ AN (37°) ≠ SAE 45° — flare angles must match exactly. Measure thread pitch with gauge — visual identification is unreliable ✓ BROKER TIP Always use thread sealant (PTFE tape or pipe compound) on tapered threads (NPT/BSPT). JIC/AN flare fittings seal metal-to-metal — never use tape on flare connections PARTSTABLE TECHNICAL DRAWING — NOT TO SCALE
KEY FEATURES
•
NOMINAL THREAD SIZE: 0.4375 INCHES IN
•
THREAD CLASS: 3B
•
NOMINAL TUBE OUTSIDE DIAMETER: 0.250 INCHES IN
•
WIDTH ACROSS FLATS: 0.558 INCHES MINIMUM AND 0.565 INCHES MAXIMUM IN
•
THREAD SERIES: UNIFIED NATIONAL JOINT FINE (UNJF)
•
THREAD DIRECTION: RIGHT-HAND
•
THREAD QUANTITY PER INCH: 20.0
•
SEAT ANGLE: 45.0 DEGREES NOMINAL
TECHNICAL CHARACTERISTICS (FLIS)
NOMINAL THREAD SIZE0.4375 INCHES IN
THREAD CLASS3B
NOMINAL TUBE OUTSIDE DIAMETER0.250 INCHES IN
WIDTH ACROSS FLATS0.558 INCHES MINIMUM AND 0.565 INCHES MAXIMUM IN
THREAD SERIESUNIFIED NATIONAL JOINT FINE (UNJF)
THREAD DIRECTIONRIGHT-HAND
THREAD QUANTITY PER INCH20.0
SEAT ANGLE45.0 DEGREES NOMINAL
SMALLEST INSIDE DIAMETER0.300 INCHES MINIMUM AND 0.305 INCHES MAXIMUM IN
END ITEM IDENTIFICATIONPSP BLK20 A K
VERIFIED SUBSTITUTES & CROSS-REFERENCES 3
SAE-AS18280Interchangeable
interchangeable cross-reference
interchangeable
MS21921W4Interchangeable
interchangeable cross-reference
interchangeable
MS21921D4Interchangeable
interchangeable cross-reference
interchangeable
LIFECYCLE
StatusACTIVE
AvailabilityOEM and secondary market
RoHS CompliantEAR99Not HAZMAT
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FREQUENTLY ASKED QUESTIONS
What is AS21921-4W?
AS21921-4W is a NUT,TUBE COUPLING.
What parts can replace AS21921-4W?
There are 3 known substitutes for AS21921-4W: SAE-AS18280, MS21921W4, MS21921D4. Substitute compatibility should be verified for your specific system.
What is the NSN for AS21921-4W?
AS21921-4W is cataloged in the Federal Logistics Information System (FLIS) under NSN 4730-01-667-6443. 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