Bolt Dimensions & Thread Sizes (Imperial)
Comprehensive table of standard imperial bolt sizes with diameters, thread pitch, tapping, and clearance information
Imperial Bolt Size Chart
| Thread Size | Major Diameter (in) | Minor Diameter (in) | Threads per Inch (TPI) | Pitch Diameter (in) | Tapping Drill Diameter (in) | Clearance Hole Diameter (in) |
|---|---|---|---|---|---|---|
| #0-80 | 0.060 | 0.049 | 80 | 0.054 | 0.046 | 0.073 |
| #2-56 | 0.086 | 0.073 | 56 | 0.079 | 0.073 | 0.106 |
| #4-40 | 0.112 | 0.098 | 40 | 0.105 | 0.099 | 0.138 |
| #6-32 | 0.138 | 0.120 | 32 | 0.127 | 0.120 | 0.164 |
| #8-32 | 0.164 | 0.140 | 32 | 0.152 | 0.139 | 0.190 |
| #10-24 | 0.190 | 0.164 | 24 | 0.172 | 0.166 | 0.216 |
| 1/4-20 | 0.250 | 0.215 | 20 | 0.225 | 0.201 | 0.281 |
| 5/16-18 | 0.3125 | 0.270 | 18 | 0.292 | 0.266 | 0.344 |
| 3/8-16 | 0.375 | 0.313 | 16 | 0.344 | 0.312 | 0.406 |
| 1/2-13 | 0.500 | 0.438 | 13 | 0.469 | 0.453 | 0.563 |
| 5/8-11 | 0.625 | 0.562 | 11 | 0.594 | 0.578 | 0.688 |
| 3/4-10 | 0.750 | 0.688 | 10 | 0.719 | 0.703 | 0.844 |
| 7/8-9 | 0.875 | 0.813 | 9 | 0.844 | 0.828 | 1.000 |
| 1-8 | 1.000 | 0.938 | 8 | 0.969 | 0.953 | 1.125 |
About Imperial Bolt Dimensions & Thread Sizes
This comprehensive imperial bolt dimensions and thread size reference provides standard U.S. and SAE bolt specifications used in mechanical design, manufacturing, and assembly. The table includes thread size, major and minor diameters, threads per inch (TPI), pitch diameter, tapping drill diameters, and clearance hole diameters — essential data for precision engineering and fastener selection.
Accurate knowledge of bolt dimensions ensures proper thread engagement, correct fit between mating components, and reliable fastening performance under load. These values are widely used in mechanical engineering, fabrication, maintenance, and production environments where adherence to standard U.S. fastener dimensions is critical.
Imperial Bolt Property Definitions
- Thread Size – The standard bolt designation (e.g., 1/4-20, 3/8-16) defining nominal diameter and thread pitch.
- Major Diameter (in) – The external crest diameter of the bolt thread; determines compatibility with nuts and tapped holes.
- Minor Diameter (in) – The root diameter at the base of the thread; influences tensile and shear strength.
- Threads per Inch (TPI) – The number of threads in one inch; indicates coarse or fine thread series for a given bolt size.
- Pitch Diameter (in) – The theoretical diameter where the thread thickness equals the groove width, ensuring proper thread fit.
- Tapping Drill Diameter (in) – Recommended drill size for producing internal threads that match the bolt’s external thread.
- Clearance Hole Diameter (in) – The free-fit hole diameter allowing a bolt to pass through without thread engagement.
Applications and Design Use
The imperial bolt size chart supports engineering design, fabrication, and maintenance operations by ensuring consistent thread engagement, correct hole sizing, and structural reliability. It is particularly valuable in machinery design, automotive engineering, aerospace applications, and industrial assembly.
Engineers, designers, and technicians can use this dataset to verify thread compatibility, select proper drilling tools, and ensure compliance with SAE, ASME, and ANSI bolt standards. By referencing these values, professionals can achieve accurate assembly alignment, minimize failure risks, and maintain mechanical integrity in fastening systems.
This page serves as a quick engineering reference for imperial fasteners, offering easy access to bolt thread dimensions and tolerances for high-precision design and quality manufacturing.