ASME B18.3 Hex Socket Countersunk Head Screw
ASME B18.3 hex socket countersunk head screws feature a conical countersunk head and internal hexagon socket, combining flush installation with convenient top-side tightening. When installed in a properly prepared countersunk hole, the head sits within the mating surface instead of remaining above it, helping maintain a smooth surface and reducing interference with adjacent components.
The machine screw design is suitable for threaded holes or compatible nuts and is available in alloy steel and stainless steel options. Alloy steel versions can provide the higher mechanical strength required for demanding assemblies, while stainless steel versions offer improved corrosion resistance for applications exposed to moisture or other corrosive conditions. With their flush-fitting head, internal hex drive, and standardized inch-thread configuration, these screws are well suited for fixtures, machine components, panels, covers, mounting plates, and other assemblies where the fastener head needs to remain recessed below or level with the surrounding surface.
Specification:
| Item | Specification |
|---|---|
| Standard | ANSI/ASME B18.3F |
| Head Type | Countersunk head |
| Drive Type | Internal Hexagon Socket |
| Thread System | Unified Inch |
| Thread Standard | ASME B1.1 |
| Thread Series | UNC/UNF |
| Size Range | 2#-1/2" |
| Material | Carbon Steel,Alloy Steel,Stainless Steel |
| Alloy Steel Standard | ASTM F835 |
| Stainless Steel Standard | ASTM F879 |
| Surface Treatment | Black Oxidation,Zinc Plated,Dacromet,Bright Finish,Passivation |
Dimension Chart:
| Thread Diameter | #2 | #3 | #4 | #5 | #6 | #8 | #10 | #12 | 1/4 | 5/16 | 3/8 | 7/16 | 1/2 |
| P | 56 | 48 | 40 | 40 | 32 | 32 | 24 | 24 | 20 | 18 | 16 | 14 | 13 |
| dk max | 0.197 | 0.226 | 0.255 | 0.281 | 0.307 | 0.359 | 0.411 | 0.45 | 0.531 | 0.656 | 0.781 | 0.844 | 0.938 |
| dk min | 0.168 | 0.193 | 0.218 | 0.24 | 0.263 | 0.311 | 0.359 | 0.41 | 0.48 | 0.6 | 0.72 | 0.781 | 0.872 |
| kk | 0.064 | 0.073 | 0.083 | 0.09 | 0.097 | 0.112 | 0.127 | 0.135 | 0.161 | 0.198 | 0.234 | 0.234 | 0.251 |
| s | 0.05 | 0.062 | 0.062 | 0.078 | 0.078 | 0.094 | 0.125 | 0.125 | 0.156 | 0.188 | 0.219 | 0.25 | 0.312 |
| t min | 0.038 | 0.044 | 0.055 | 0.061 | 0.066 | 0.076 | 0.087 | 0.094 | 0.111 | 0.135 | 0.159 | 0.159 | 0.172 |
Mechanical Proeprty:
Alloy Steel ASME B18.3 Socket Countersunk Head Screw— ASTM F835
ASME B18.3 hex socket countersunk head machine screws made from alloy steel are specified according to ASTM F835 for mechanical properties. These screws are quenched and tempered to meet the strength requirements for high-strength fastening applications. Key mechanical properties include tensile strength, yield strength, hardness and elongation, which help determine their suitability for assemblies subject to demanding mechanical loads.
Stainless Steel ASME B18.3 Socket Countersunk Head Screw— ASTM F879
ASME B18.3 hex socket countersunk head machine screws made from stainless steel are covered by ASTM F879, which specifies the applicable material and mechanical requirements. Depending on the stainless steel alloy group and condition, these screws offer different combinations of mechanical strength and corrosion resistance. Relevant properties include tensile strength, yield strength, elongation and hardness.