[1] The nominal size may not match any dimension of the product, but within the domain of that product the nominal size may correspond to a large number of highly standardized dimensions and tolerances.
When considering the engineering tolerance between a shaft (or bolt) going through a hole in some other part (such as a nut), both the shaft (or bolt) have the same nominal size (also called the basic size),[2][3] [4] but all the holes are physically larger and all the shafts are physically smaller in order that any shaft (or bolt) of a given nominal size can fit into any hole of the same nominal size.
As techniques improve beyond this threshold, it will become clear that 1 inch is not the real value of the gauge block length, but some other number approximates it.
For example, both 1⁄2 inch and 15 millimetres (0.59 in) copper pipe is actually the same pipe which has a nominal internal diameter of 1⁄2 an inch and a nominal external diameter of 15 millimetres[6] (diameter is always internal in the imperial measurement system and always external in metric).
A machine is designed to operate at some particular condition, often stated on the device's nameplate.