MEASUREMENT FOR SHAPE OF SCREW

PURPOSE:To enable a hihgly accurate measurement by a method wherein reflected lights are captured from a light beam projected onto the surface of a screw being moved along the axial length thereof and the heigthwise displacement of the screw and the quantity of reflected lights from the surface thereof are detected to make a correction corresponding to the displacement and the quantity of the reflected lights detected. CONSTITUTION:The shape of a screw section 10a of an oil well pipe is measured with a measuring apparatus 30 using a displacement gauge 31 utilizing a fine- diameter light beam such as laser beam. The displacement gauge 31 is positioned on the side of a pair of turning rollers 2 and moved along the axial length of a coupling 10 with a scanning mechanism. In other words, the displacement gauge 31 is supported on a stage 32, which is provided with a means 32a of driving the coupling 10 along the axial length thereof and a position detector 32b. The position detector 32b herein used shall be those with the measuring accuracy of several mum order, for example, a magnetic type digital scale and an inductosyn.