Precision gauge blocks named after their Swedish inventor, sold in sets such as 81 or 88 pieces that can be combined to build almost any length in steps of a tenth. Their lapped faces are so flat they wring together, held by a thin film of oil or moisture and molecular attraction. Jo blocks calibrate mics, height gauges and indicators, and set sine bars and comparators.
Wring up a 2.4375 stack out of the Jo blocks and check the mic against it before you touch the bearing journals.
Wipe them, wring them, use them and unwring them the same day; a stack left wrung overnight can weld itself together.
Also heard as
- gauge blocks
- Johansson blocks
- Jos
Related terms
Mic
Short for micrometer, pronounced mike, and the verb for measuring a part with one.
Surface plate
A thick slab of granite or cast iron, lapped flat, that every height check and layout line is measured from.
Tenth
One ten-thousandth of an inch (0.0001 in, about 2.5 microns), the unit of precision grinding and fits.
Test indicator
A lever-type dial indicator with a swiveling stylus, used to align setups and compare surfaces.