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MS21921-4K — NUT,TUBE COUPLING

✓ Government record, cited
— · HOSE FITTING
PRODUCT OVERVIEW

MS21921-4K: NUT,TUBE COUPLING.

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 part is cataloged in the U.S.

Government catalog 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
MS21921-4K
NSN: 4730-00-034-1411
FSC: 4730 — Hose, Pipe, Tube, Lubrication, and Railing Fittings
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: MS21921-4K · 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
•
LENGTH TO SHOULDER: 0.547 INCHES NOMINAL IN
•
WIDTH ACROSS FLATS: 0.562 INCHES NOMINAL IN
•
THREAD SERIES: UNIFIED NATIONAL JOINT FINE (UNJF)
•
MATERIAL DOCUMENT AND CLASSIFICATION: QQ-S-763 FED SPEC SINGLE MATERIAL RESPONSE OVERALL
•
SEAT ANGLE: 45.00 DEGREES NOMINAL
•
THREAD DIRECTION: RIGHT-HAND
•
NOMINAL THREAD SIZE: 0.438 INCHES IN
•
SPECIFICATION/STANDARD DATA: 96906-MS21921 GOVERNMENT STANDARD
TECHNICAL CHARACTERISTICS
LENGTH TO SHOULDER0.547 INCHES NOMINAL IN
WIDTH ACROSS FLATS0.562 INCHES NOMINAL IN
THREAD SERIESUNIFIED NATIONAL JOINT FINE (UNJF)
MATERIAL DOCUMENT AND CLASSIFICATIONQQ-S-763 FED SPEC SINGLE MATERIAL RESPONSE OVERALL
SEAT ANGLE45.00 DEGREES NOMINAL
THREAD DIRECTIONRIGHT-HAND
NOMINAL THREAD SIZE0.438 INCHES IN
SPECIFICATION/STANDARD DATA96906-MS21921 GOVERNMENT STANDARD
NUT HEIGHT0.531 INCHES NOMINAL IN
SURFACE TREATMENTPASSIVATE OVERALL
OTHER ITEMS IN FSC 4730 — Hose, Pipe, Tube, Lubrication, and Railing Fittings
Items in the same Federal Supply class. No interchangeability or substitution relationship is implied.
4730-00-000-1895 4730-00-000-4289 4730-00-000-4445 4730-00-000-8373 4730-00-000-8897 4730-00-001-0007 4730-00-001-0008
SUBSTITUTES & CROSS-REFERENCES 3
AS21921-4KReference document
Same NSN cross-reference
Reference document — Secondary reference
AS21921Reference document
Same NSN cross-reference
Reference document — Secondary reference
SAE-AS18280Reference document
Same NSN cross-reference
Reference document — Design control — primary reference
LIFECYCLE
NSN statusActive· U.S. Government catalog
Acquisition advice: Insurance item — stocked against contingency demandNo demilitarization required
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FREQUENTLY ASKED QUESTIONS
What is MS21921-4K?
MS21921-4K is a NUT,TUBE COUPLING.
What parts can replace MS21921-4K?
There are 3 known substitutes for MS21921-4K: AS21921-4K, AS21921, SAE-AS18280. Substitute compatibility should be verified for your specific system.
What is the NSN for MS21921-4K?
MS21921-4K is cataloged in the U.S. Government catalog under NSN 4730-00-034-1411. 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.