Screw & Bolt Thread Size Chart (Metric & UNC)
Metric (M2–M24) and UNC (#4–3/4") thread chart with pitch, threads per inch, tap drill and clearance hole sizes — plus a tap drill calculator for any thread.
How to use
- 1Look up the thread size in the chart.
- 2For non-standard threads, enter the major diameter and pitch (or TPI) to get the tap drill size.
How it's calculated
Tap drill ≈ major diameter − pitch (about 75% thread engagement). For inch threads: tap drill ≈ major diameter − 1 ÷ TPI.
Frequently asked questions
What does M8 × 1.25 mean?
An 8 mm major diameter with 1.25 mm between threads. Coarse pitch is the default if no pitch is given (M8 = M8 × 1.25).
What's a clearance hole?
A hole the bolt passes through freely without engaging threads — slightly larger than the bolt's diameter.
What's the difference between UNC and UNF?
UNC is coarse (fewer threads per inch, faster to assemble); UNF is fine (more threads, stronger in thin material and more resistant to vibration).