4 mm may refer to:
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4 mm caliber
This is a list of firearm cartridges which have bullets in the to caliber
In guns, particularly firearms, but not #As a measurement of length, artillery, where a different definition may apply, caliber (or calibre; sometimes abbreviated ...
, gun cartridges between 4–5 mm diameter
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4 mm scale
4 mm scale is the most popular model railway scale used in the United Kingdom. The term refers to the use of 4 millimeters on the model equating to a distance of 1 foot (305 mm) on the prototype (1:76.2). It is also used for military m ...
, in rail transport modelling, 1:76.2 scale with rails 16.5 mm apart, representing standard gauge in Britain
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