Fine wire such as is used for lamp filaments is passed over a flat horizontal anvil and its diameter at any position along its length is measured quite locally by lowering into contact with it a small horizontal cylinder having its axis transverse to the wire. The cylinder is attached to one end of a system of compound levers, so arranged that the vertical displacements of the cylinder are finally magnified about 15,000 times on a glass scale. The latter has a range of only about 0.0004 in., but wires of any diameter can be measured by varying the size of the standard block gauge which constitutes the upper surface of the anvil.An arrangement is provided for rotating the wire through definite angles in order to test the uniformity of diameter round any section.Variations in the diameter of a wire can be measured to a millionth of an inch, and its absolute diameter determined at any point to within an accuracy of ± 0.000,003 in.The possibility of using the machine for continuous measurements along a spool of wire is considered.