ANSI/ASME B18.3 Hex Socket Countersunk Head Machine Screw
ANSI/ASME B18.3F Hex Socket Countersunk Head Machine 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:
The specification of ANSI/ASME B18.3F Hex Socket Countersunk Head Machine Screws covers the dimensional and functional requirements needed for consistent installation and interchangeability. The product standard defines the applicable head, socket, length, and dimensional characteristics, while the Unified inch thread requirements ensure compatibility with matching internally or externally threaded components. For material and mechanical requirements, the applicable specification depends on the selected material. Alloy steel and stainless steel versions are available with their respective material and mechanical requirements, allowing the fastener to be selected according to the load, operating environment, and service conditions. When specifying a screw, the nominal diameter, thread series, length, countersunk dimensions, material, mechanical requirements, and surface finish should be considered together to ensure proper fit and performance.
| Item | Specification |
|---|---|
| Standard | ANSI/ASME B18.3F |
| Product Type | Hex Socket Countersunk Head Machine Screw |
| 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 of ANSI/ASME B18.3F Hex Socket Countersunk Head Machine Screw:
The dimension chart provides the key measurements required to select and verify the screw for a countersunk installation. Nominal diameter and length determine the basic fastening size, while the head diameter, countersunk dimensions, and socket size are important for proper seating, tool access, and clearance around the fastener. All dimensions should be selected according to the applicable ANSI/ASME B18.3F size.
| 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 |
- RELATED BOLT LISTS:
- ANSI/ASME B18.3 Stainless Steel American Standard Countersunk Head Torx Screw
- ANSI/ASME B18.3 Stainless Steel Hexagon Socket Button Head Cap Screws
- American Standard ASME/ANSI B18.3 Hexagon Socket Head Cap Screws
- ASME/ANSI B18.6.3 Cross Recessed Pan Head Machine Screws
- DIN7991 Stainless Steel Hex Socket Countersunk Head Cap Screws
- ISO7380 Stainless Steel Hexagon Socket Button Head Screws
- DIN963 90° Stainless Steel Slotted Countersunk Head Screws
- DIN965 Stainless Steel Cross Recessed Countersunk Head Screws
- DIN84 Stainless Steel Slotted Cheese Head Screws
- DIN7971 Stainless Steel Slotted Pan Head Tapping Screws
Application of ANSI/ASME B18.3 Hexagon Socket Button Head Cap Screws:
Fixtures & Mounting Plates
Hex Socket Countersunk Head Machine Screws are suitable for fixtures, mounting plates, jigs, brackets, and equipment panels where the fastener head needs to sit flush with the surrounding surface. The recessed head helps minimize interference with adjacent components and provides a clean mounting surface.
Machine Components & Moving Surfaces
The flush-fitting design is useful for machine covers, sliding components, guide plates, guards, and mechanical parts where a protruding screw head could interfere with movement or reduce available clearance. The internal hex socket also allows tightening from the exposed side of the assembly.
Equipment & Corrosion-Resistant Assemblies
These screws can be used in industrial equipment, processing machinery, outdoor assemblies, and other applications where both flush installation and material selection are important. Alloy steel versions are suitable for higher-strength connections, while stainless steel options can be selected for improved corrosion resistance.