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This page is dedicated to Sir Joseph Whitworth, Baronet (Born 21 December 1803 – Died 22 January 1887).

He is credited with many different innovations when it comes to measurement, from his methods for scraping
to his early micrometers to measure accurately. Additionally he set out the first standard screw threads in the world.

He is credited as giving us in the machine shop the "thou" or the thousandths of a inch as a base unit of measurement.
In a machine shop most measurements are used in the 1x10^-3 from the inch. A reamed 1/4 inch hole is labeled on a drawing as ".250" or "Two Hundred and Fifty Thou", generally machined to "two tenths" of a inch using a reamer. In this case 2 tenths actually refers to 2 tenths of a thou not of a inch. There is a significant difference between the normal 0.1 tenth of a inch people think of and the machinist's .0001" tenth.

None the less his story is a interesting and good read. As a start I suggest downloading the PDF in the attachment section of this page and read it. Plenty of good information in there for anyone interested on how such precise
measurements were done without the technology of today.

Dimitrios Simitas,
Feb 15, 2010, 2:53 PM