The FF-S-86 federal specification governs socket-head cap screws bought through the federal supply system: high-strength precision fasteners driven into tapped holes by a hexagon or spline key. It is maintained by the Defense Logistics Agency, and the current revision is FF-S-86H, issued June 7, 2021. The original document dates to November 4, 1953, and has been reissued repeatedly since. One clarification up front, because the confusion is common: FF-S-86 is not a padlock specification. Federal padlocks fall under separate documents such as FF-P-110J for changeable combination padlocks used with classified material.
Screw Types Covered
The specification’s full title is “Federal Specification: Screw, Cap, Socket-Head,” and it applies to externally threaded fasteners used where a job needs high strength, a compact profile, or a head that sits recessed below a surface. Procurement documents identify the fastener by type and size, and the wrong type is the wrong screw.
- Type I is the hexagon socket head cap screw, a cylindrical head with an internal hex socket. This is the common configuration.
- Type IV is the socket flat countersunk head cap screw, used where the head must sit flush with or below the surface.
- Type VI is a socket head cap screw with dimensional differences from Type I for specific application needs.
- Type VIII is the socket button head cap screw, a low-profile dome shape that still takes a hex key.
Sizes start at #0 (0.060-inch nominal body diameter) and scale upward, with dimensions conforming to ASME B18.3.
Approved Materials
FF-S-86 divides acceptable materials into four families, and the environment the screw will live in drives the choice.
Alloy Steel
Alloy steel is the workhorse category. Seven grades are permitted: 4137, 4140, 4142, 4145, 4340, 8740, and 5137M. The steel must be produced using fine grain practice per ASTM E112, and boron-containing alloys are prohibited. Grade 4140 screws are heat treated under AMS 2759/1.
Corrosion-Resistant Steel
For moisture, chemicals, or saltwater, the specification allows austenitic corrosion-resistant steels in types 302, 304, 304L, 305, 316, 316L, and 384, each manufactured to the chemistries in ASTM A493. These trade some raw strength for far better corrosion life.
Heat and Corrosion-Resistant Steel
Where temperatures run high, the specification calls for A286 iron-base superalloy screws made to AMS 5731 or AMS 5853. Cold working and precipitation hardening are permitted to reach the required mechanical properties. This is the material for engine and exhaust hardware.
Non-Ferrous Materials
The specification also covers nickel-copper alloy, nickel-copper-aluminum alloy, Inconel 625 or 686, and titanium screws. These serve applications where magnetism, weight, or aggressive chemistry rules steel out entirely, and they are used mostly in aerospace and naval work.
Coatings
Five coating options are recognized under FF-S-86: cadmium plating, zinc plating, zinc-nickel plating, phosphate coating, and black chemical finish. Cadmium offers strong corrosion protection and lubricity but has been restricted by environmental regulation in many non-military uses. Zinc is a cheaper alternative with solid corrosion resistance, and zinc-nickel outperforms plain zinc and is increasingly used as a cadmium replacement. Phosphate is generally a base for oil or a supplementary coating on alloy steel, and black chemical finish gives a dark appearance with minimal dimensional change.
One detail catches manufacturers off guard. When a coating is applied to Class 2A threads, the maximum material limit after coating must still meet Class 3A. Screws that ignore this end up not fitting their intended holes.
Thread and Dimensional Requirements
Unless the buyer specifies otherwise, threads conform to the UNC, UNRC, UNF, UNRF, or UN8 series in FED-STD-H28/2. The default thread class is 3A for nominal diameters from 0.060 through 1.000 inch, and Class 2A for diameters above 1.000 inch. Class 3A gives a tighter fit with less allowance, which matters in precision assemblies where vibration can back a looser fastener out.
Dimensional requirements (head diameter, head height, socket depth, body diameter) reference ASME B18.3. Proof load testing follows ASTM F606/F606M Method 1 for Type I and Type VI cylindrical socket head cap screws.
Testing and Traceability
A manufacturer cannot simply self-certify and ship. Documented proof load testing, hardness testing, and dimensional inspection are required to verify both material properties and finished-product performance.
Every manufacturer must also stamp a registered logo directly onto the fastener, giving each screw a permanent link back to its source. The Defense Logistics Agency maintains the logo registry under MIL-HDBK-57, and logos must be approved before product enters the federal supply chain.1Defense Logistics Agency. Consumable Hardware
When a Qualified Products List Applies
Some federal specifications require a product to appear on a Qualified Products List before agencies may buy it. A QPL is a government-maintained roster of products that have passed qualification testing for the specification in question. Being listed is not a government endorsement, and it does not relieve the manufacturer of ongoing compliance.2Naval Facilities Engineering Systems Command. Federal Qualified Products List of Products Qualified Under Federal Specification FF-L-2740
Under DLA policy, QPL qualification is justified when testing would take more than 30 days, when it requires specialized equipment not commonly available, or when the item is emergency life-saving equipment.1Defense Logistics Agency. Consumable Hardware Manufacturers pursuing qualification should register with the ASSIST database and contact the Preparing Activity listed for the specification.
Extra Rules on Military Orders
Screws bought for military use are limited to the configurations documented in specific National Aerospace Standards, including NAS1351, NAS1352, NASM16995, and NASM16996. Each of these fixes a combination of head type, material, thread series, and finish approved for defense applications.
Defense procurement also triggers DFARS material sourcing rules, so the steel must meet domestic sourcing requirements. Manufacturers who supply both commercial and military markets generally need separate material tracking to prove compliance on the military side.
What Happens If a Manufacturer Ships Noncompliant Screws
Delivering nonconforming fasteners has consequences past losing the contract. The Federal Acquisition Regulation authorizes debarment when a contractor willfully fails to perform in accordance with contract terms or shows a pattern of unsatisfactory performance, which bars the contractor from new federal contracts.3Acquisition.GOV. Subpart 9.4 – Debarment, Suspension, and Ineligibility
Falsifying test results or knowingly shipping noncompliant product also exposes the manufacturer to civil liability under the False Claims Act, which imposes treble damages and a per-claim penalty adjusted annually. As of 2025, that penalty runs from $14,308 to $28,619 per false claim.4Federal Register. Civil Monetary Penalties Inflation Adjustments for 2025 On a lot of thousands of screws shipped with falsified certifications, per-claim numbers scale quickly. A fraud conviction, false statements, or destruction of records tied to a government contract can trigger debarment on its own.3Acquisition.GOV. Subpart 9.4 – Debarment, Suspension, and Ineligibility
Revision History and Working From the Current Issue
FF-S-86 has been revised repeatedly since 1953 to add materials, tighten tolerances, and track updated industry standards. Major milestones include FF-S-86E (May 29, 1987), FF-S-86F (January 7, 2020), and the current FF-S-86H (June 7, 2021). Contracts reference the latest effective issue, so before beginning production a manufacturer should confirm they are working from the current revision. Copies of earlier revisions stay available through standards databases, and building to a superseded version is a compliance failure waiting to be found.