Diameter, TPI, and pilot hole reference
| Screw Size | Major Ø (in) | TPI | Pilot Drill (in) |
|---|
Numbered sizes (#0–#14) use a gauge number instead of a direct measurement — higher number means a thicker screw. For example, #8-32 means gauge #8 diameter with 32 threads per inch (TPI).
Fractional sizes (1/4", 5/16", 3/8", etc.) state the major diameter directly, followed by TPI, such as 1/4-20.
TPI (Threads Per Inch) tells you how coarse or fine the thread is. Coarse threads (lower TPI) grip faster and resist stripping in soft materials; fine threads (higher TPI) hold better in metal and thin materials.
Pilot hole drill size is the recommended drill bit diameter for a pilot hole in wood before driving the screw — slightly smaller than the screw's major diameter so threads can bite.
Click any row to highlight it for quick reference. Use the search box to filter by size, and switch units with the Imperial/Metric toggle.