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.
DHEA (dehydroepiandrosterone) is the most abundant steroid hormone in the body, and is a direct precursor of testosterone. DHEA levels decrease with age, an 80 year old person will have only 10% of the DHEA produced during peak years or early adulthood. Thus, DHEA supplementation can be particularly helpful to manage low testosterone levels in both men and women. Patients supplementing with DHEA for low testosterone will notice improvement in the testosterone levels but need to be monitored closely.