Thread Measuring Wire Calibration

Reference ASME B89.1.17-2001

Attributes to be inspected:

  • Diameter – Use high magnification comparator or measuring instrument with adjustable measuring force. .0000020” resolution or better is required. Use a cylindrical anvil.
  • Roundness – Use Vee anvil with 60 degree included anvil. Cylindrical masters and a normalizing plate are required.

Suggestions for improved accuracy:

Calibrate only in the central middle half of the thread measuring wire.

Thread measuring wires are calibrated on a functional basis so as to compensate for deformation when the wires are being used.

  • Wire diameter is measured with the wire placed over a cylindrical anvil of a known size by a flat round contact point.
  • The effects of errors in roundness are determined by noting the changes in diameter measurement utilizing a vee anvil and taking measurements around and along the wire.

Refer to ASME B89.1.17-2001 for measuring force and contact point configurations.

Wires must be unrestrained during measurement. They should be held in place by the specified measuring contact force only.

The set of 3 wires in a set must be calibrated at the same time to ensure the commonality of size standard is met. Each wire in a set must have the same diameter within .000010”.

Handle all thread measuring wires with care. Wires should be handled with soft tip tweezers.

Allow adequate time for thread measuring wires to normalize. Use a normalizing plate adjacent to the measuring equipment.

Measurement Uncertainty

AttributeNormal Laboratory ConditionsOptimum Laboratory Conditions
Wire Diameter +/-0.000025”/ 0.00064mm +/-0.000015”/ 0.00038mm
Wire Straightness/Roundness 0.000015”/0.000383mm 0.000005”/0.000130mm