BS 959:2008

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

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 Table1 and Table2. NOTE Attention is drawn to the fact that metric dimensions are not necessarily direct conversions of the imperial dimensions. Table1 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+ Table2 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: a 150mm or 300mm or 6 in or 12 in micrometer unit, fitted with a micrometer of 25mm or 1 in range, and having rounded terminal faces; 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.