Part Number
Socket Head Cap Screw · OEM / vendor part number · NSN 5305-00-983-6661
| Part number | 3M991-4-6 |
|---|---|
| Specification family | OEM / vendor part number |
| Item name | Socket Head Cap Screw |
| Alternate references | MS16998-44; MS16998-44-XX002-0279; XX002-0279; AJA01-C06 |
| Unit of issue | EA |
| Cross-referenced NSN | 5305-00-983-6661 |
| Federal Supply Class (FSC) | 5305 — Screws |
| Unit price (USD) | $78.86 |
| Country of origin | Türkiye (Turkey) |
| Lead time | Within 90 days of order |
| Minimum order | May apply — confirm on quote |
| Documentation | Source documentation provided on all orders |
Characteristics decoded from the federal cataloging record for this socket head cap screw. Confirm controlling dimensions against your drawing or standard sheet before ordering.
| Fastener Length | 0.785 Inches Minimum And 0.815 Inches Maximum |
|---|---|
| Hardness Rating | 36.0 Rockwell C Minimum And 45.0 Rockwell C Maximum Overall |
| Head Style | Flat Chamfer |
| Material | Steel Overall |
| Nominal Thread Diameter | 0.250 Inches |
| Surface Treatment | Cadmium And Chromate Overall |
| Thread Class | 3A |
| Thread Series Designator | Unf |
Externally threaded fasteners designed to be turned to assemble or adjust parts, including machine screws, cap screws, socket-head cap screws, set screws, self-tapping and thread-forming screws. This is the largest single class in the U.S. supply system and covers a vast range of thread sizes, drive types, head styles, and materials.
Reading the part number. 3M991-4-6 is a vendor part number for this socket head cap screw. If your documentation lists a different reference for the same item, include it on the quote and we will confirm the cross-reference.
Price in context. Across the 2,357 items we currently stock in FSC 5305 (Screws), published unit prices run from $0.03 to $14,752.17. At $78.86, this item sits well above the class median of $10.52 — typical of assemblies and higher-value line items in this class.
Who orders 3M991-4-6. Aircraft owners and MRO shops replacing standard hardware, machine shops and OEMs filling a bill of materials, and government contractors sourcing against NSN 5305-00-983-6661. You can order by part number or by stock number — it is the same item, the same published price, and the same quote form.
Applicable standards. ASME B18.3 / B18.6.3, MIL-DTL / NASM / MS and AN series, ISO metric threads; common materials include carbon and alloy steel, 300/400-series stainless, and A2/A4 stainless per ISO 3506.
Need this part modified, or a similar part made to your print? See our U.S.-based CNC machining services and aerospace machining capability.
Country of origin: Türkiye (Turkey). Turkey is a NATO ally and a normal-trade-relations partner of the United States, and Turkish-origin end items are eligible for a wide range of U.S. federal and DLA procurements.
TAA note: Turkey is not a Trade Agreements Act (TAA) designated country, so these items are generally not eligible for TAA-covered solicitations. They are offerable under the Buy American Act and many non-TAA DLA buys. Buyers are responsible for confirming the origin requirements of their specific solicitation.
Full country-of-origin and source documentation is provided with every order. Fulfillment within 90 days of order. Minimum order may apply.
Items are supplied as stock mil-spec / commercial hardware with source documentation and country-of-origin paperwork on every order. Parts are not supplied with an FAA Form 8130-3 airworthiness tag unless expressly stated on the quote. Buyers installing hardware on certificated aircraft are responsible for acceptance under their own maintenance program, repair station procedures, or owner/operator authority.
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