PartsTable TECHNICAL DATA SHEET
JULY 2026Technical Data Sheet

A78-121Washer,key

Borg-Warner Corp Marvel-Schebler/tillotson Div · NSN 5310-00-209-4125 · FSC 5310 · No Item Name Available
Verified by PartsTable
NSN 5310-00-209-4125 — this item is cataloged by the U.S. Government under National Stock Number 5310-00-209-4125. Primary manufacturer part number: A78-121.
Features
  • Washer,key — FSC 5310
  • Hardness Rating: 30.0 ROCKWELL B MINIMUM AND 50.0 ROCKWELL B MAXIMUM
  • Outside Diameter: 0.370 INCHES MINIMUM AND 0.380 INCHES MAXIMUM IN
  • Hole Diameter: 0.191 INCHES MINIMUM AND 0.196 INCHES MAXIMUM IN
  • External Key Quantity: 6
  • Surface Treatment: CADMIUM OVERALL
  • Material: STEEL OVERALL
  • Overall Distance Including Keys: 0.557 INCHES MINIMUM AND 0.567 INCHES MAXIMUM IN
Applications
  • Structural fastening and assembly
  • Equipment mounting
  • Panel and housing attachment
  • Applications requiring Steel Overall construction
General Description

The Washer,key, cataloged under National Stock Number 5310-00-209-4125, is classified within Federal Supply Class 5310 (No Item Name Available) of the Hardware and Abrasives group. The primary manufacturer of record is Borg-Warner Corp Marvel-Schebler/tillotson Div. Government technical data includes 11 verified specifications, sourced from the Federal Logistics Information System (FLIS). This item has 2 commercial cross-references from 1 manufacturer, enabling identification through both NSN and commercial part number lookups. 5 verified substitutes exist in the FLIS interchangeability database. Current acquisition status: Cancelled.

Technical Specifications
ParameterValue
NSN5310-00-209-4125
Primary Part NumberA78-121
Item NameWasher,key
FSC / FSG5310 / 53 — No Item Name Available
ManufacturerBorg-Warner Corp Marvel-Schebler/tillotson Div
StatusCANCELLED
Hardness Rating30.0 ROCKWELL B MINIMUM AND 50.0 ROCKWELL B MAXIMUM
Outside Diameter0.370 INCHES MINIMUM AND 0.380 INCHES MAXIMUM IN
Hole Diameter0.191 INCHES MINIMUM AND 0.196 INCHES MAXIMUM IN
External Key Quantity6
Surface TreatmentCADMIUM OVERALL
MaterialSTEEL OVERALL
Overall Distance Including Keys0.557 INCHES MINIMUM AND 0.567 INCHES MAXIMUM IN
Material Thickness0.026 INCHES MINIMUM AND 0.036 INCHES MAXIMUM IN
Style DesignatorKEY
Surface Treatment Document and ClassificationAN-QQ-P-421 FED SPEC SINGLE TREATMENT RESPONSE OVERALL
External Straight Key Width0.104 INCHES MINIMUM AND 0.114 INCHES MAXIMUM IN
Lifecycle & Compliance
Acquisition StatusCANCELLED
HAZMATNo
Verified Substitutes 5
2815-00-036-5413 INTERCHANGEABLE
Tee,water
5975-00-284-640278121 INTERCHANGEABLE
Rack,cable,interior
Ant Company of VA, the
2990-00-303-7804T-2759 INTERCHANGEABLE
Muffler,exhaust
Cummins Filtration Inc.
5950-00-910-6419 INTERCHANGEABLE
Transformer
5915-01-177-9108AT-504-1070 INTERCHANGEABLE
Filter,radio Frequency Interfere
Airtronics, Llc
Cross-Reference Index
Part NumberManufacturer
A78-121 Borg-Warner Corp Marvel-Schebler/tillotson Div (USA)
78-121 Borg-Warner Corp Marvel-Schebler/tillotson Div (USA)
Related Parts
2815-00-036-5413INTERCHANGEABLE
TEE,WATER
5975-00-284-6402INTERCHANGEABLE
RACK,CABLE,INTERIOR
78121
2990-00-303-7804INTERCHANGEABLE
MUFFLER,EXHAUST
T-2759
5950-00-910-6419INTERCHANGEABLE
TRANSFORMER
5915-01-177-9108INTERCHANGEABLE
FILTER,RADIO FREQUENCY INTERFERE
AT-504-1070

Frequently Asked Questions

What is NSN 5310-00-209-4125?

NSN 5310-00-209-4125 is a Washer,key, manufactured by Borg-Warner Corp Marvel-Schebler/tillotson Div, classified under FSC 5310 (No Item Name Available). Status: cancelled.

What are the part numbers for NSN 5310-00-209-4125?

NSN 5310-00-209-4125 has 2 cross-referenced part numbers: A78-121 (Borg-Warner Corp Marvel-Schebler/tillotson Div), 78-121 (Borg-Warner Corp Marvel-Schebler/tillotson Div).

What NSN replaces 5310-00-209-4125?

There are 5 known substitutes for 5310-00-209-4125: 2815-00-036-5413, 5975-00-284-6402, 2990-00-303-7804 and 2 more. Verify interchangeability with system specifications before substitution.

What are the specifications of A78-121?

Key specifications for A78-121: Hardness Rating: 30.0 ROCKWELL B MINIMUM AND 50.0 ROCKWELL B MAXIMUM; Outside Diameter: 0.370 INCHES MINIMUM AND 0.380 INCHES MAXIMUM IN; Hole Diameter: 0.191 INCHES MINIMUM AND 0.196 INCHES MAXIMUM IN; External Key Quantity: 6. 11 total characteristics are documented in the Federal Logistics Information System.

Is NSN 5310-00-209-4125 still in active supply?

NSN 5310-00-209-4125 is currently cancelled. Check with the Defense Logistics Agency for current availability and authorized substitutes.

Validated with multiple authoritative sources, including Government, OEM, and Certified sources.
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