A Short Course On Measuring Pitch Diameters

Do you know that bolts, tapes, dies and other helically threaded components are characterized by various parameters? These parameters include depth, angle, pitch, major and minor diameters, whereby the pitch diameter holds the most significance amongst these parameters. Read on to find out more about the importance and the process of measuring pitch diameters!

What is a Pitch Diameter?

To many of us, the effective diameter, also known as the pitch diameter, refers to the diameter of the cylinder as it cuts the midpoint of both the major and minor diameters known as the pitch line. The pitch diameter is an important property that governs the compatibility between two threaded parts, such as nuts and bolts and if they can be successfully mated with each other. Moreover, they are also used as a crucial reference for other relevant thread measurements.

Measurement of Pitch Diameter

Due to the large susceptibility of pitch diameters to measurement errors, unique measuring equipment must be used in order to obtain an accurate reading. Although there exist many types of techniques to measure pitch diameter, there exist three most commonly utilized methods, namely the three-wire measurement method, the optical comparators and specialized micrometer screw gages which ensures the accuracy of your reading!

Three-Wire Method

The three-wire method makes use of a traditional, flat anvil micrometer screw gage to measure pitch diameter. Three separate wires of pre-measured diameter would be placed within the pitch of the threads before the gage of the wire is chosen. This enables the wires to stay in contact with the pitch line while simultaneously extending beyond the outside diameter of the thread. With another micrometer screw gage, the distance between the wires on the opposite sides are measured and used as inputs in prescribed formulas to derive the pitch diameter.

Optical Comparators

Optical comparators make use of the fundamental basis of optics and light to determine the pitch diameter. A magnified silhouette of the threaded object is projected on a screen and a specialized software would be used for image analysis and to obtain the pitch diameter. Through the use of optical comparators, it would result in a high degree of accuracy in pitch diameter measurements. However, a downside of it would be its expensive cost!

Specialized Micrometer Screw Gages

A commonly used instrument would be a form of micrometer screw gage known as a thread mic or a pitch mic. It was designed for the purpose of measuring the pitch diameters of cutting threading tools. To make use of this instrument, the ratchet of the micrometer is turned continuously until the spindle comes into contact with the thread flanks. The pitch diameter can then be read off from the micrometer scales. This method provides an efficient and accurate, but yet a low-cost way of measuring the pitch diameter!

At Willrich Precision Instrument, we provide a large selection of thread gages that would definitely meet the rigorous needs of your business! Browse through our exciting inventory and shop for quality thread gages today. If you need assistance with any product purchase, call us at 866-945-5742 or email us at sales@willrich.com today.

by George Chitos

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