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Technical Data Sheet
PartsTable / COMPONENT / AS21921-4K
AS21921-4K ✓ 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: STEEL COMP 316 OVERALL, nut_style: TUBE COUPLING, nut_height: 0.531 INCHES NOMINAL IN, seat_angle: 45.00 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 4730-00-034-1411, 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
AS21921-4K
NSN: 4730-00-034-1411
FSC: 4730
CAGE: 0U583 — SAE INTERNATIONAL DBA SAE INTERNATIONAL (USA)
SPECIFICATIONS
materialSTEEL COMP 316 OVERALL
nut_styleTUBE COUPLING
nut_height0.531 INCHES NOMINAL IN
seat_angle45.00 DEGREES NOMINAL
thread_class3B
thread_seriesUNIFIED NATIONAL JOINT FINE (UNJF)
thread_directionRIGHT-HAND
surface_treatmentPASSIVATE OVERALL
length_to_shoulder0.547 INCHES NOMINAL IN
width_across_flats0.562 INCHES NOMINAL IN
nominal_thread_size0.438 INCHES IN
smallest_inside_diameter0.300 INCHES NOMINAL IN
NSN4730-00-034-1411
COMPONENT DIAGRAM
HOSE FITTING — THREAD TYPE IS CRITICAL END A: — STRAIGHT END B: — SPECIFICATIONS Thread: — Material: — Pressure: — PN: AS21921-4K · 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
•
SURFACE TREATMENT: PASSIVATE OVERALL
•
SEAT ANGLE: 45.00 DEGREES NOMINAL
•
SMALLEST INSIDE DIAMETER: 0.300 INCHES NOMINAL IN
•
SPECIFICATION/STANDARD DATA: 96906-MS21921 GOVERNMENT STANDARD
•
NOMINAL THREAD SIZE: 0.438 INCHES IN
•
NUT STYLE: TUBE COUPLING
•
THREAD SERIES: UNIFIED NATIONAL JOINT FINE (UNJF)
•
NOMINAL TUBE OUTSIDE DIAMETER: 0.250 INCHES IN
TECHNICAL CHARACTERISTICS (FLIS)
SURFACE TREATMENTPASSIVATE OVERALL
SEAT ANGLE45.00 DEGREES NOMINAL
SMALLEST INSIDE DIAMETER0.300 INCHES NOMINAL IN
SPECIFICATION/STANDARD DATA96906-MS21921 GOVERNMENT STANDARD
NOMINAL THREAD SIZE0.438 INCHES IN
NUT STYLETUBE COUPLING
THREAD SERIESUNIFIED NATIONAL JOINT FINE (UNJF)
NOMINAL TUBE OUTSIDE DIAMETER0.250 INCHES IN
LENGTH TO SHOULDER0.547 INCHES NOMINAL IN
THREAD QUANTITY PER INCH20
VERIFIED SUBSTITUTES & CROSS-REFERENCES 3
MS21921-4KInterchangeable
Same NIIN cross-reference
interchangeable
AS21921Interchangeable
Same NIIN cross-reference
interchangeable
SAE-AS18280Interchangeable
Same NIIN cross-reference
interchangeable
LIFECYCLE
StatusACTIVE
AvailabilityOEM and secondary market
RoHS CompliantEAR99Not HAZMAT
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FREQUENTLY ASKED QUESTIONS
What is AS21921-4K?
AS21921-4K is a NUT,TUBE COUPLING.
What parts can replace AS21921-4K?
There are 3 known substitutes for AS21921-4K: MS21921-4K, AS21921, SAE-AS18280. Substitute compatibility should be verified for your specific system.
What is the NSN for AS21921-4K?
AS21921-4K is cataloged in the Federal Logistics Information System (FLIS) under NSN 4730-00-034-1411. 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