ASME/ANSI B18.3 Countersunk Head Torx Screw
ASME/ANSI B18.3 Countersunk Head Torx Screws are designed for applications requiring a low-profile, flush-mounted fastening point combined with controlled Torx drive engagement. The countersunk head seats into a matching countersunk hole so that the head remains at or below the surrounding surface, making the screw suitable for assemblies where protruding fastener heads could interfere with adjacent components.
The six-lobe Torx recess provides a positive driver interface, allowing installation torque to be transferred through multiple contact surfaces and reducing the tendency of the driver to slip from the recess during tightening. This is particularly useful when consistent installation torque is required across repeated assembly operations. For mechanical performance, alloy steel versions can be specified to ASTM F835 and stainless steel versions to ASTM F879, where applicable. The appropriate material and mechanical property requirement should be selected according to the required strength, corrosion resistance, installation conditions, and service environment.
Specification:
| Item | Specification |
|---|---|
| Standard | ASME/ANSI B18.3 |
| Product Type | Countersunk Head Screw |
| Head Style | Flat Countersunk Head |
| Drive Type | Torx/6-Lobe |
| Thread System | Inch |
| Thread Series | UNC/UNF |
| Material | Alloy Steel,Stainless Steel |
| Alloy Steel Standard | ASTM F835 |
| Stainless Steel Standard | ASTM F879 |
| Surface Treatment | Zinc Plated, Black Oxidation,Bright Finish,Passivation |
Dimension Chart of ASME B18.3 Countersunk Head Torx Screw:
| Thread Diameter | 2# | 4# | 5# | 6# | 8# | 10# | 1/4 | 5/16 | 3/8 | 7/16 | 1/2 | 5/8 | 3/4 | 7/8 | 1 | |
| d | 0.086 | 0.112 | 0.125 | 0.138 | 0.164 | 0.19 | 0.25 | 0.3125 | 0.375 | 0.4375 | 0.5 | 0.625 | 0.75 | 0.875 | 1 | |
| PP | UNC | 56 | 40 | 40 | 32 | 32 | 24 | 20 | 18 | 16 | 14 | 13 | 11 | 10 | 9 | 8 |
| UNF | 64 | 48 | 44 | 40 | 36 | 32 | 28 | 24 | 24 | 20 | 20 | 18 | 16 | 14 | 12 | |
| UNEF | - | - | - | - | - | - | 32 | 32 | 32 | 28 | 28 | 24 | 20 | 20 | 20 | |
| ds | max | 0.086 | 0.112 | 0.125 | 0.138 | 0.164 | 0.19 | 0.25 | 0.3125 | 0.375 | 0.4375 | 0.5 | 0.625 | 0.75 | 0.875 | 1 |
| min | 0.0822 | 0.1075 | 0.1202 | 0.1329 | 0.1585 | 0.184 | 0.2435 | 0.3053 | 0.3678 | 0.4294 | 0.4919 | 0.6163 | 0.7406 | 0.8647 | 0.9886 | |
| dk | max | 0.197 | 0.255 | 0.281 | 0.307 | 0.359 | 0.411 | 0.531 | 0.656 | 0.781 | 0.844 | 0.938 | 1.188 | 1.438 | 1.688 | 1.938 |
| min | 0.168 | 0.218 | 0.24 | 0.263 | 0.311 | 0.359 | 0.48 | 0.6 | 0.72 | 0.781 | 0.872 | 1.112 | 1.355 | 1.604 | 1.841 | |
| k | Ref | 0.064 | 0.083 | 0.09 | 0.097 | 0.112 | 0.127 | 0.161 | 0.198 | 0.234 | 0.234 | 0.251 | 0.324 | 0.396 | 0.468 | 0.54 |
| A | Ref | 0.094 | 0.111 | 0.111 | 0.132 | 0.155 | 0.178 | 0.221 | 0.266 | 0.312 | 0.352 | 0.352 | 0.446 | 0.529 | 0.619 | 0.795 |
| t | Ref | 0.03 | 0.035 | 0.04 | 0.04 | 0.045 | 0.05 | 0.065 | 0.087 | 0.105 | 0.1 | 0.119 | 0.135 | 0.205 | 0.265 | 0.285 |
| b | Ref | 0.62 | 0.75 | 0.75 | 0.75 | 0.88 | 0.88 | 1 | 1.12 | 1.25 | 1.38 | 1.5 | 1.75 | 2 | 2.25 | 2.5 |
| α | ±2° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° | 82° |
| Slot No. | T8 | T10 | T10 | T15 | T20 | T25 | T30 | T40 | T45 | T50 | T50 | T55 | T60 | T70 | T90 |
- RELATED SCREW LISTS:
- Torx Countersunk Screw
- ISO14581 Torx Countersunk Screw
- Button Head Torx Screw
- ISO7380-3 Torx Button Screw
- ASME B18.3 Torx Button Screw
- ISO14583 Torx Pan Head Screw
- Cylindrical Head Torx Screw with Pin
- Cuntersunk Head Torx Screws with Pin
- Button Head Torx Screws with Pin
- ISO14584 Torx Raised Countersunk Head Screws
Mechanical Property:
ASTM F835 – Alloy Steel ASME B18.3 countersunk head torx screws
ASME B18.3 Countersunk Head Torx Screws manufactured from alloy steel can be specified to ASTM F835, Standard Specification for Alloy Steel Socket Button and Flat Countersunk Head Cap Screws. This specification covers quenched and tempered alloy steel fasteners intended for high-strength applications. Mechanical property requirements include tensile strength, yield strength, hardness, elongation, and reduction of area.
ASTM F879 – Stainless Steel ASME B18.3 Countersunk head torx screw
ASME B18.3 Countersunk Head Torx Screws manufactured from stainless steel can be specified to ASTM F879, Standard Specification for Stainless Steel Socket Button, Low and Flat Countersunk Head Cap Screws. This specification establishes chemical composition and mechanical property requirements for stainless steel fasteners intended for applications requiring general corrosion resistance.