Preferred Values
Engineers influence the measurements and other characteristics of products under development - although constrained by considerations of functionality, usability, compatibility, safety and cost, there is usually some flexibility in the exact choice for many dimensions. International standards define preferred values (also called preferred numbers) for choosing exact product dimensions within such constraints.
Using preferred numbers increases the probability that other designers will independently make the same choices. This can be useful where the chosen dimension affects compatibility - for example, if the inner diameters of cooking pots or the distances between mounting screws in wall fixtures are chosen from a series of preferred numbers, then it should be more likely that old pot lids and wall-plug holes can be reused when the original product is replaced.
Standard preferred numbers are related to each other on a logarithmic scale, and this helps to rationalize the number of different sizes of things like nails or screws that need to be manufactured or kept in stock.
Find out more: