The Seat,valve, cataloged under National Stock Number 4820-01-181-8657, is classified within Federal Supply Class 4820 (Valves, Nonpowered) of the Valves group. The manufacturer of record is Huntington Ingalls Inc Div Newport News Shipbuilding. Government technical data includes 9 specifications, cited from the U.S. Government catalog. The record lists 1 manufacturer part number for this item, enabling identification through both NSN and commercial part number lookups. 3 additional reference documents (drawings, advisory and superseded references) are recorded in the U.S. Government catalog. 3 items share a part number with this NSN in the catalog (possible match — not a government interchangeability claim). Current acquisition status: Active.
| Parameter | Value |
|---|---|
| NSN | 4820-01-181-8657 |
| Primary Part Number | 6553-255 PIECE 9 |
| Item Name | Seat,valve |
| FSC / FSG | 4820 / 48 — Valves, Nonpowered |
| Manufacturer | Huntington Ingalls Inc Div Newport News Shipbuilding |
| Status | ACTIVE |
| Thread Length | 0.500 INCHES NOMINAL SINGLE THREADED PORTION IN |
| Style Designator | PLAIN THREADED |
| Body Inside Diameter | 4.250 INCHES NOMINAL IN |
| Nominal Thread Size | 5.375 INCHES SINGLE THREADED PORTION IN |
| Thread Class | 2A SINGLE THREADED PORTION A |
| Thread Quantity Per Inch | 12 SINGLE THREADED PORTION |
| Material | NICKEL ALLOY OVERALL |
| Thread Series Designator | UN SINGLE THREADED PORTION |
| Seating Surface Shape | FLAT |
| Acquisition Status | ACTIVE |
| DEMIL Code | DEMIL A — No Demilitarization Required |
| Hazard | No hazard code in the DLA record (HMIC N) |
| Criticality Code | X |
| Part Number | Manufacturer |
|---|---|
| 6553-255 PIECE 9 | Huntington Ingalls Inc Div Newport News Shipbuilding (USA) |
| Reference | Meaning |
|---|---|
| 208-4325303 PIECE 9 | 3/2 Design control — primary reference U.S. Government activity |
| 208-4325303 | D/9 Drawing number reference only U.S. Government activity |
| 6553-255 | D/9 Drawing number reference only Huntington Ingalls Inc Div Newport News Shipbuilding |
NSN 4820-01-181-8657 is a Seat,valve, manufactured by Huntington Ingalls Inc Div Newport News Shipbuilding, classified under FSC 4820, Valves, Nonpowered. Status: active.
NSN 4820-01-181-8657 has 1 manufacturer part number on file: 6553-255 PIECE 9 (Huntington Ingalls Inc Div Newport News Shipbuilding).
3 possible matches (shared part number, not a government interchangeability claim): 4820-01-415-3220, 4820-01-415-8298, 4820-01-416-0449. Verify interchangeability with system specifications before substitution.
Key specifications for 6553-255 PIECE 9: Overall Height: 0.634 INCHES NOMINAL IN; Thread Length: 0.500 INCHES NOMINAL SINGLE THREADED PORTION IN; Style Designator: PLAIN THREADED; Body Inside Diameter: 4.250 INCHES NOMINAL IN. 9 specifications are documented in the U.S. Government catalog.
No hazard code in the DLA record (HMIC N). Hazard information on this page is shown exactly as it appears in the DLA record.
U.S. Government catalog: edition PUBLOGDVD v12.0.0 (OCT 2026), edition date 2026-10-01, retrieved 2026-10-16.
U.S. Government catalog: edition PUBLOGDVD v12.0.0 (OCT 2026), edition date 2026-10-01, retrieved 2026-10-18.