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Acme Threads 3 Wire Measuring of Pitch Diameter

A very common way to measure the pitch diameter of 29° Acme screw threads is with the 3 wire thread measuring method.  In this thread measuring method a measurement is taken across 3 predefined pins or “wires” placed in the thread v usually with a micrometer or to a less accurate degree with calipers.  Once the measurement is taken an accurate pitch diameter can be determined by subtracting a “constant” from the measured dimension to obtain the actual thread pitch diameter.

Just Added to Web Machinist!  3 Wire Thread Measuring Calculator”.  Quickly calculate dimensions when using the 3 wire thread pitch measuring method for both inch and metric threads.

The Web Machinist 3 Wire Thread Measuring Calculator above is available in the Web Machinist software program seen below:

The first step in using the 3 wire Acme Thread measuring method is to determine the “Best Wire Size” to be used in calculating the Acme Threads Pitch Diameter.

To determine the “Best Wire Size” simply apply this formula:

Divide .51645 by the number of threads per inch.

Example: To determine the “Best Wire Size” for a 29° Acme Thread with 16 TPI (Threads Per Inch),

Divide .51645 by 16 = .032278125”

Of course you can round the result down to a better obtainable wire size such as .03228” or .0323” or .032”

TPI (Threads Per Inch) =


Wire Size =



For 60 Degree Thread 3 Wire Measuring Click Here

For Metric 30° Trapezoidal Threads 3 Wire Measuring Click Here

Of Course an easier way to calculate the Best Wire Size for an Acme Thread is to use the Acme 3 wire Measuring Calculator included in the Web Machinist Software (below).

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