ANSI/ASME B18.6.3 Six-Lobe Countersunk Machine Screws

ANSI/ASME B18.6.3 Six-Lobe Countersunk Machine Screws are inch-series machine screws with a flat countersunk head and six-lobe internal drive. The countersunk head sits flush with the mating surface when installed in a properly prepared countersunk hole, making this screw type suitable where a low-profile surface is required.

These machine screws are commonly used in machinery, equipment, electrical enclosures, metal assemblies, consumer products, and other applications requiring a recessed fastening point. The six-lobe drive provides positive tool engagement and is available in standard and center-pin configurations. The center-pin version is commonly used where tamper resistance or restricted access is required.

B18.6.3 covers the dimensional requirements for machine screws in the inch series. The six-lobe countersunk configuration is specified as a hexalobular socket countersunk flat head screw, with an 82° countersunk head geometry in the applicable B18.6.3 configuration. Common inch thread forms include UNC and UNF, with size and length selected according to the application.

Material options can include carbon steel, stainless steel, and applicable nonferrous materials, depending on the specified product configuration. Surface finishes may include plain, zinc plated, black oxide, phosphate and oil, or other finishes appropriate to the material and specification.

For applications requiring a specific drive configuration, material, thread, finish, size, or packaging method, specifications can be defined according to the required product configuration.