As correctly pointed out by ASimpson, there are classification of fits which are application specific. He lists the metric version, imperial are equivalents noting 1.0 inch = 25.4 mm. There are several good references on this, look to the web. But the Machinist Handbook does discuss this, at least in the 23rd edition.
How does Dhea work? DHEA is a parent hormone produced by the adrenal glands near the kidneys and in the liver. In men, DHEA is also secreted by the testes. It is changed in the body to a hormone called androstenedione. Androstenedione is then changed into the major male and female hormones.
C. DHEA levels may decrease with age. Early evidence in older adults suggests that DHEA may help protect against age-related declines in physical function. Research suggests that low levels of hormones such as DHEA may predict mortality (death) in older men; however, these data have been criticized.