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Bolt Thread Identifier

Identifies the closest metric thread from a caliper measurement, with pitch, spanner size and hex key size.

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In short Bolt Thread Identifier is a free online tool on inputtesthub.com that identifies the closest metric thread from a caliper measurement, with pitch, spanner size and hex key size. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.

How to use the Bolt Thread Identifier

  1. Enter your figures in the input fields.
  2. The result updates as you type, together with the full working.
  3. Check the breakdown table to see exactly how the number was reached.

About the Bolt Thread Identifier

The Bolt Thread Identifier identifies the closest metric thread from a caliper measurement, with pitch, spanner size and hex key size. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.

What people use it for

  • Identifying a bolt you have pulled out of something.
  • Finding the spanner size before walking to the toolbox.
  • Checking whether a bolt is metric or imperial.

Details

M610 mm spanner
M813 mm spanner
M1017 mm spanner
M1219 mm spanner
⅜" imperial9.53 mm — sits between M8 and M10

The maths behind it

This tool uses Compares your measurement against the nominal outside diameters of standard metric threads and returns the closest, with its coarse pitch. Every intermediate value is shown on screen, so the result can be checked by hand.

Measure across the thread crests, not the valleys — a worn thread reads small and pushes you a size down. A reading almost exactly between two sizes usually means an imperial bolt, and forcing a metric nut onto one strips both.

Frequently asked questions

Is the Bolt Thread Identifier free?
It is free, with no account, no trial and no daily cap. Every calculators tool on inputtesthub.com works the same way: open the page and use it.
Is what I paste into the Bolt Thread Identifier stored?
No. The Bolt Thread Identifier runs entirely in your browser using JavaScript. Your input never reaches inputtesthub.com or any third party — open your browser's Network tab while you use it and you will see no request go out.
What is the equation behind the Bolt Thread Identifier?
It uses Compares your measurement against the nominal outside diameters of standard metric threads and returns the closest, with its coarse pitch. The full working is printed under the result, so you can follow every step rather than trusting a black box.
When would I actually need the Bolt Thread Identifier?
The most common reasons people reach for it: identifying a bolt you have pulled out of something. Finding the spanner size before walking to the toolbox. Checking whether a bolt is metric or imperial. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything to watch out for?
Measure across the thread crests, not the valleys — a worn thread reads small and pushes you a size down. A reading almost exactly between two sizes usually means an imperial bolt, and forcing a metric nut onto one strips both.
Which values should I know?
M6 is 10 mm spanner. M8 is 13 mm spanner. M10 is 17 mm spanner. These are printed on the page itself, so you do not have to take them on trust.
Can I rely on this for exact work?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.

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