Ha ha, there's all kinds of historical weirdness related to screws and threads.
Did I bore you about pipe sizing already?
HISTORY OF PIPING SIZE TERMS
Pipe sizes can be confusing because the terminology may relate to historical dimensions. For example, a half-inch iron pipe does not have any dimension that is a half inch. Initially, a half inch pipe did have an inner diameter of 0.5 inches (13 mm)—but it also had thick walls. As technology improved, thinner walls became possible, but the outside diameter stayed the same so it could mate with existing older pipe, increasing the inner diameter beyond half an inch.
OUTSIDE DIAMETER
The outside diameters of pipes are described by the “Nominal Pipe Size”, shown in specifications as
NPS and often incorrectly called “inches”. In more recent times with the introduction of the metric
system and with the usage of the same pipes in Europe, a metric version has been developed called
DN, or “Diameter Nominal”, often incorrectly called “millimetres” and also incorrectly referred to as Nominal Bore or NB. The pipe sizing system did originate with an understanding that then standard pipe sizes when used at the then most typical wall thickness gave an internal diameter approximately equal to the nominal size. With the current multiplicity of wall thicknesses available the Nominal bore concept has long since ceased to be relevant, and in fact is now misleading. All pipe is specified by outside diameter, never by inside diameter.
Fuck Israel