Machinist shorthand for a ten-thousandth of an inch, the scale of bearing fits, ground pins and gauge work. Holding tenths takes a grinder or a very stiff machine, a temperature-stable part and gauge, and a mic or indicator that reads to tenths. At this level heat matters: a 4 inch steel part grows about a tenth for every 4 degrees Fahrenheit, so parts are measured cold, not straight off the machine.
Bearing fit is plus two tenths, minus nothing, so let it cool on the plate before you mic it.
To an outsider a tenth sounds like 0.1 in; on the floor it always means 0.0001 in, and mixing them up marks you instantly.
Also heard as
- ten-thousandth
- tenths
Do not mix it up with
- Thou: A thou is one-thousandth of an inch, ten times bigger than a tenth.
Related terms
Thou
One thousandth of an inch (0.001 in, about 25 microns), the everyday unit of machining talk in inch shops.
Mic
Short for micrometer, pronounced mike, and the verb for measuring a part with one.
Jo blocks
Shop name for gauge blocks: lapped steel or ceramic blocks, accurate to millionths, stacked to make any length.
Test indicator
A lever-type dial indicator with a swiveling stylus, used to align setups and compare surfaces.