Every number on this site is traceable to a named standard revision or to a stated formula. This page explains how that works, and where the limits are.
Last updated 2026-09-23
A reference for dimensional, material and conversion data used in mechanical and electrical work. It exists because the alternatives are awkward: the governing standards are authoritative but written for design rather than lookup and cost money to obtain; supplier pages are scattered and rarely cite a source; search results are often a photograph of a table.
The aim here is narrower than “all engineering data”. It is to publish a small number of data sets properly — sourced, cross-checked, dated, and citable — rather than a large number loosely.
Three routes are used, in this order of preference:
Where a standard defines a geometry mathematically, values are computed rather than transcribed. The unified thread form is the clearest case: pitch, pitch diameter, both minor diameters and the tensile stress area are all closed-form functions of the nominal diameter and the pitch. Computing them means the values are self-consistent by construction, and it means the published figures are ours rather than a copy of a copyrighted table.
Where a data set is fixed rather than derivable, it is taken from a source that can be cited openly — military standards (US government works carry no copyright), published material property handbooks, or a standard whose dimensional values are factual.
Before anything is published it is compared against at least one independent source. The cross-check source is named on the page it applies to.
On standards and copyright. Facts are not copyrightable — the pitch diameter of a 1/4-20 thread is a fact, and it is the same fact whoever writes it down. A standard's document is protected, and none is reproduced here. What is published is the dimensional data, attributed to the standard that defines it, in tables of our own construction.
Every data page carries the same three mechanisms:
If a value does not check out, the contact page explains what to send for a correction to be applied.
Standards are revised. A dimension that was correct against the 2003 revision of a standard may differ in the 2019 revision. Every page therefore states the revision it was built against and the date the data was last verified, and any change to the underlying data is recorded at build time.
This is deliberately conservative: a reference site that does not say when its data was checked is asking to be trusted without evidence.
Errors on a reference site are worse than gaps, because a wrong number gets used. Corrections with a traceable source are prioritised and applied quickly. See the contact page for what to include.
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