This British Standard applies to the following types of external
micrometers.
a) External micrometers having a frame holding a micrometer
spindle and nut on one side opposite a fixed anvil on the
other, with individual measuring ranges of: 0-13 mm; 25 mm
(e.g. 0-25 mm, 25-50 mm, etc., up to 575-600 mm) and 0-? in;
1 in (e.g., 0-1 in, 1-2 in, etc., up to 23-24 in).
b) External micrometers having a frame holding a micrometer
spindle and nut on one side opposite an anvil on the other, and
providing for two or more alternative ranges of measurement
effected by means of interchangeable or sliding anvils, with
individual measuring ranges of:
? 0-50 mm, 0-100 mm, 100-200 mm, 200-300 mm, 300-400 mm,
400-500 mm and 500?600 mm; or
? 0-2 in, 0-4 in, 4-8 in, 8-12 in, 12-16 in, 16-20 in and 20-24 in.
c) Setting gauges for micrometers above 25 mm or 1 in.
NOTE Attention is drawn to the fact that metric dimensions are not
necessarily direct conversions of the imperial dimensions.
BS 870:2008 history
2011BS EN ISO 3611:2010 Geometrical product specifications (GPS). Dimensional measuring equipment. Micrometers for external measurements. Design and metrological characteristics
2008BS 870:2008 Specification for external micrometers
1950BS 870:1950 Specification for external micrometers