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Metric and unified inch threads on three A4 pages

A free three-page A4 size chart for bolt and screw threads: the metric threads M1 to M64 of ISO 261 with pitch and minor diameters, stress area and tap drill, and the unified UNC and UNF threads of ASME B1.1 from #0 to 4 in.

bolt-screw-size-chart.pdf

Bolt and Screw Size Chart cover
Type
Chart
Format
PDF
Download size
61 KB PDF
Price
Free
License
Free to use
What's inside

What the chart covers

  • Metric threads

    21 first-choice sizes with coarse and fine pitches, pitch and minor diameters and stress area, from ISO 261.

  • Unified threads

    UNC #1 to 4 in and UNF #0 to 1 1/2 in with pitch and minor diameter and tensile stress area, from ASME B1.1.

  • Thread profile

    The 60 degree basic profile with the formulas for every diameter.

  • Stress area

    In square millimetres for every size, with the load a thread carries.

  • Inch against metric

    Seven inch sizes against the nearest metric thread.

  • Read from the standards

    Pitches and inch dimensions are read from ISO 261 and ASME B1.1; computed values are labelled.

How to use it

Using the chart

  1. 01

    Download the PDF

    Enter your name and email and the link arrives at once.

  2. 02

    Find the size

    Look up the metric or the inch thread on page 1 or 2.

  3. 03

    Check the load

    Take the stress area and the bolt class and read the load on page 3.

A free three-page A4 size chart for bolt and screw threads: the 21 first-choice ISO metric threads M1 to M64 with coarse and fine pitches, pitch and minor diameters, stress area and tap drill, and the unified inch threads UNC and UNF from #0 to 4 in with pitch and minor diameters and tensile stress area. The pitches and the inch dimensions are read from ISO 261:1998 and ASME B1.1-2019; the metric diameters and stress areas are computed from the 60° basic profile with the formulas printed on the chart, so the numbers on the wall and on the screen cannot disagree.

Page 1 of the bolt and screw size chart: metric threads M1 to M64, thread geometry and an M10 worked examplePage 1 of the bolt and screw size chart: metric threads M1 to M64, thread geometry and an M10 worked example
Page 1: the metric threads, the basic profile, the thread geometry formulas and an M10×1.5 worked example.

What is on the chart

  • Page 1. The 21 first-choice metric threads M1 to M64 with coarse pitch, fine pitches, pitch diameter, minor diameter, stress area and tap drill, the 60° basic profile, the geometry formulas, an M10×1.5 load example and the stress area of M10 with four pitches.
  • Page 2. The unified coarse (UNC, #1 to 4 in) and fine (UNF, #0 to 1 1/2 in) series of ASME B1.1 Tables 6 and 7: major, pitch and minor diameter, threads per inch and tensile stress area in square inches and square millimetres, with the inch thread formulas.
  • Page 3. How a thread is written, the pitch and threads-per-inch conversion, the tensile load of a thread, seven inch sizes against the nearest metric thread, and a log-log plot of stress area against size.
Page 2 of the chart: unified coarse and fine thread tables of ASME B1.1Page 2 of the chart: unified coarse and fine thread tables of ASME B1.1
Page 2: UNC and UNF, each row computed from the standard’s table values.

Metric threads

Table of the 21 first-choice metric threads M1 to M64 with pitches, diameters, stress area and tap drillTable of the 21 first-choice metric threads M1 to M64 with pitches, diameters, stress area and tap drill
ISO 261:1998 Table 2, first choice. A pitch in brackets, such as the 3 on M30, is the one to avoid where possible. The stress area is shown to three significant figures; ISO 898-1:2013 Table 5 prints it for M3 to M39.

The 60° basic profile fixes every diameter from the major diameter dd and the pitch PP:

H=32Pd2=d−0.6495 Pd3=d−1.2269 PAs=π4(d2+d32)2H = \tfrac{\sqrt{3}}{2}P \qquad d_2 = d - 0.6495\,P \qquad d_3 = d - 1.2269\,P \qquad A_s = \tfrac{\pi}{4}\left(\tfrac{d_2 + d_3}{2}\right)^2
The 60 degree basic thread profile with pitch P, height H and the major, pitch and root diameter linesThe 60 degree basic thread profile with pitch P, height H and the major, pitch and root diameter lines
The basic profile has depth H1=58H=0.5413 PH_1 = \tfrac{5}{8}H = 0.5413\,P down to d1d_1; an external thread is rounded to the minor diameter d3d_3, which makes its depth h3=1724H=0.6134 Ph_3 = \tfrac{17}{24}H = 0.6134\,P.

Unified inch threads

Table of the 33 unified coarse UNC sizes from #1 to 4 inTable of the 33 unified coarse UNC sizes from #1 to 4 in
ASME B1.1-2019 Table 6. Millimetre values are computed with 1 in = 25.4 mm. Table 6 prints 4 threads per inch for 2 1/4 UNC, but the series table and the tolerance tables of the same standard give 2 1/4–4.5 UNC, so that row is computed with 4.5 threads per inch and marked.
Table of the 24 unified fine UNF sizes from #0 to 1 1/2 inTable of the 24 unified fine UNF sizes from #0 to 1 1/2 in
ASME B1.1-2019 Table 7. The tensile stress area follows As=π4(D−0.9743n)2A_s = \tfrac{\pi}{4}\left(D - \tfrac{0.9743}{n}\right)^2 with nn threads per inch.

How a thread is written

The parts of the callouts M10 x 1.5 and 1/4-20 UNCThe parts of the callouts M10 x 1.5 and 1/4-20 UNC
A metric thread is M, the diameter in millimetres and the pitch (left out for coarse). An inch thread is the size or screw number, the threads per inch and the series. A metric and an inch thread of the same major diameter are not interchangeable.
Seven inch sizes against the nearest metric threadSeven inch sizes against the nearest metric thread
Computed with 1 in = 25.4 mm, rounded half up; the difference is taken from the printed diameter, so every row adds up.

Coarse or fine, and how much load

Stress area of M10 with four pitches and of 1/2 in UNC against UNFStress area of M10 with four pitches and of 1/2 in UNC against UNF
A finer pitch cuts the thread less deep, so the bolt keeps more steel: M10×0.75 has 17.0 % more stress area than M10×1.5, and 1/2–20 UNF has 12.7 % more than 1/2–13 UNC.

The load a thread carries follows from the stress area and the stress of the bolt class:

F=σ As(F in N when σ in MPa and As in mm2)F = \sigma\,A_s \qquad (F\ \text{in N when}\ \sigma\ \text{in MPa and}\ A_s\ \text{in mm}^2)

At an assumed stress of 100 MPa an M10 gives 5.80 kN and a 1/4–20 UNC (As=20.52 mm2A_s = 20.52\ \text{mm}^2) gives 2.05 kN. Take the stress from the property class of the bolt: ISO 898-1 for metric bolts, SAE J429 or ASTM grades for inch bolts.

Log-log plot of stress area against size for the metric coarse and the unified coarse threadsLog-log plot of stress area against size for the metric coarse and the unified coarse threads
Stress area grows with the square of the diameter: doubling the size gives about four times the area.

Where the numbers come from

The pitches come from ISO 261:1998 Table 2 and the inch dimensions from ASME B1.1-2019 Tables 6 and 7, read by script from the standards. The metric pitch and minor diameters, stress areas, tap drills and every inch-to-millimetre value are computed, and each computed value is labelled on the chart. After the PDF is built, a second script reads it back and compares every printed number with the data.

The chart is a reading aid. For a drawing, a contract or an inspection report, ISO 261, ISO 262, ISO 898-1 and ASME B1.1 are the authority. Second and third choice metric diameters (M14, M18, M22 and others) and sizes outside these tables are in the standards.

Questions or a design you want reviewed? Get in touch.

Preview

The chart at a glance

Page 2: the unified UNC and UNF tables.
Page 3: reading the sizes, load and the stress area plot.
The 21 first-choice metric threads.
Unified coarse threads, #1 to 4 in.
Unified fine threads, #0 to 1 1/2 in.
The 60 degree basic profile.
How a metric and an inch thread are written.
Stress area of coarse and fine pitches.
Stress area against size.
Inch sizes against the nearest metric thread.

Get the chart

About 61 KB PDF.

bolt-screw-size-chart.pdf

FAQ

Questions, answered

Is the chart free?

Yes. Enter your name and email and the download link appears at once.

Which sizes are not on the chart?

The second and third choice metric diameters (M14, M18, M22 and others), metric sizes above M64, unified sizes above 4 in and the other thread series. Use ISO 261 or ASME B1.1 for those.

Can I rely on the numbers for a contract?

Use them to design and check. For contracts and inspection reports the standards ISO 261, ISO 898-1 and ASME B1.1 are the authority.

Bolt Size ChartThread SizeISO 261ASME B1.1UNCUNFMetric ThreadStress AreaMechanical DesignFree

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