Thread and Fastener Charts (Inch and Metric)

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Reference charts for the threads and fasteners used in a workshop: Unified inch (UNC and UNF) and ISO metric thread dimensions, tap drills and clearance holes, and nails, wood screws and lag screws for woodworking and building. The thread charts are computed from the published thread formulas or taken from the same drill and clearance tables our calculators use. The nail and screw charts come from the USDA Wood Handbook, a public-domain reference from the Forest Products Laboratory. Every chart shows its formula or source so you can check a row by hand.

Charts

  • UNC and UNF thread chart: 47 inch threads from #0-80 to 1-1/2 in with TPI, major, pitch and minor diameters, stress area and tap drill.
  • Metric thread pitch chart: 36 coarse and fine metric threads, M1 to M36.
  • Tap drill chart: the 75% drill for every thread, and the thread percentage you get with the drills you have.
  • Clearance hole chart: close, normal and loose fits, inch and metric, with a hole position tolerance example.
  • Nail size chart: length and diameter of common, box and threaded nails from 3d to 90d, and withdrawal by wood species.
  • Wood screw size chart: shank and root diameter for #4 to #24, pilot and clearance holes, and withdrawal by wood species.
  • Lag screw pilot hole chart: shank and thread lead holes for 1/4 to 1 in lag screws in soft, medium and dense woods.
  • Bolt torque chart: tightening torque for SAE Grade 2, 5 and 8 and metric 8.8, 10.9 and 12.9 bolts, dry and lubricated.
  • Wrench size chart: the wrench or socket for inch, heavy hex, ISO and DIN metric bolts.
  • Drill bit size chart: number, letter, fractional and metric drills in one list with decimal and mm sizes.
  • Thread engagement chart: minimum length of thread for inch and metric bolts in steel, cast iron and aluminium.
  • Nail gun nail sizes: 23, 21, 18, 16 and 15 gauge diameters, framing nail diameters, holding power and minimum length.

Tap drill size by thread

Identify an unknown thread in three steps

  1. Measure the outside diameter of the bolt with calipers (or the inside of the nut). Expect a bolt to read a few thousandths of an inch under nominal; a reading of 0.245 in is a 1/4 in bolt, 5.9 mm is M6.
  2. Measure the pitch. A thread pitch gauge is quickest; otherwise count crests along a ruler. Inch threads are counted as threads per inch; metric threads are measured as the distance between crests in millimetres.
  3. Match both numbers in the UNC/UNF or metric chart. Watch for near-misses: 1/4-20 and M6 x 1, #10-24 and M5 x 0.8, 5/16-18 and M8 x 1.25 differ by less than you might think.

The thread profile in one paragraph

Unified and ISO metric threads share the same 60 degree basic profile. From the pitch P, the height of the fundamental triangle is H = 0.866025 P. The basic pitch diameter is the major diameter minus 0.649519 P, and the basic minor diameter of the internal thread is the major diameter minus 1.082532 P. The tensile stress area, the cross-section used to rate a bolt, is 0.7854 (D − 0.9743 P)² for inch threads and π/4 (d − 0.938194 P)² for metric. For a 1/4-20 bolt those formulas give a pitch diameter of 0.2175 in and a stress area of 0.0318 in². Real bolts and nuts are made to tolerance classes around these basic sizes.

Calculators and guides

Safety and structural use

The thread charts are for making and fitting threaded parts and do not give load ratings. The withdrawal figures on the nail, wood screw and lag screw charts are laboratory averages at failure, not design values. For anything that carries people or a structural load (deck ledgers, guards, lifting, vehicle parts), use fasteners and torque values specified by the manufacturer, the applicable code or a licensed engineer, and check your local building code.

Frequently asked questions

What is the difference between UNC, UNF and metric threads?

UNC (coarse) and UNF (fine) are the two main series of the Unified inch standard, sized in inches and threads per inch. ISO metric threads are sized in millimetres with the pitch in millimetres. All three share the same 60 degree profile but are not interchangeable.

Where do the numbers in these charts come from?

They are computed from the basic profile formulas in ASME B1.1 (inch) and ISO 68-1 (metric), and from the standard twist drill and clearance hole series, as listed under each chart.

Which thread is the most common in woodworking jigs?

1/4-20 UNC in North America (T-track bolts, knobs, threaded inserts) and M6 or M8 elsewhere.

Sources and method

Every dimension on this page is computed from the formulas below, not copied from another chart, so you can check any row by hand. Values are basic (nominal) dimensions; real parts are made to tolerance classes (2A/2B for inch, 6g/6H for metric) and are slightly smaller (bolts) or larger (nuts and tapped holes).

  1. ASME B1.1, Unified Inch Screw Threads (UN and UNR Thread Form): basic profile, pitch-diameter and minor-diameter relationships, and the tensile stress area formula. The same relationships are published in the US federal standard FED-STD-H28/2B, Screw-Thread Standards for Federal Services, Section 2 (a US Government work).
  2. ISO 68-1, ISO general purpose screw threads, basic profile; ISO 261, general plan of diameters and pitches; ISO 898-1, stress area of metric bolts.
  3. ASME B94.11M, Twist Drills: number, letter and fractional drill diameters (the drill list used by our calculators).
  4. ISO 273, Fasteners, clearance holes for bolts and screws (fine, medium, coarse series); inch close / normal / loose fits as published in the ASME B18.2.8 clearance classes and reproduced in fastener suppliers’ charts.
  5. Percentage-of-thread formula for tap drills: Machinery’s Handbook (Industrial Press), as used by our tap drill size calculator.

More thread and fastener tools

Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Spotted an error? Please let us know.