BS 959:2008

This standard BS 959:2008 Specification for internal micrometers (including stick micrometers) is classified in these ICS categories:

• 17.040.30 Measuring instruments

This standard specifies requirements for internal micrometers comprising a measuring head, extension rods with or without spacing collars, and, in the smaller sizes, a handle.

Provision is made for three sizes of measuring heads, in both metric and inch units, as shown in Table 1 and Table 2.

NOTE Attention is drawn to the fact that metric dimensions are not necessarily direct conversions of the imperial dimensions.

Table 1 Measuring heads — metric measurements

Size of head	Length of graduated scale on barrel	Usual ranges of the instrument when used with extension rods
	mm	mm
Size 1	5 or 6.5	25-50
Size 2	10 or 13	50-150
		50-200
		50-300
Size 3	25	200+

Table 2 Measuring heads — inch measurements

Size of head	Length of graduated scale on barrel	Usual ranges of the instrument when used with extension rods
	in	in
Size 1	¼	1-2
Size 2	½ or 1	2-6
		2-8
		2-12
Size 3	1	8+

This standard also covers stick micrometers, which are designed for the measurement of longer internal lengths, and comprise the following parts:

1. a 150 mm or 300 mm or 6 in or 12 in micrometer unit, fitted with a micrometer of 25 mm or 1 in range, and having rounded terminal faces;

2. a series of extension rods which, together with the micrometer unit, permit a continuous range of measurement up to the maximum length required.

Annex A gives a method of test for the accuracy of internal micrometer readings.