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Site Last Updated 8/25/14

3 Wire Thread Pitch Diameter Measuring

A very common way to measure the pitch diameter of 60° V  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.

Measurement across wires using a micrometer.

Actual thread pitch diameter determined by subtracting the constant from the measurement taken across the 3 thread wires.

Wire size used in the 3 wire thread measuring method.

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.

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

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The chart below lists the Wire Size and Constant for measuring Inch 60° V threads using the 3 wire thread measuring system:

Threads Per Inch:           Wire Size:        Constant:

48                               .018                .03596

44                               .018                .03432

40                               .018                .03235

36                               .018                .02994

32                               .024                .04494

28                               .024                .04107

27                               .024                .03992

24                               .029                .05092

20                               .029                .04370

18                               .032                .04789

16                               .040                .06587

14                               .040                .05814

13                               .045                .06838

12                               .055                .09283

11.5                            .055                .08969

11                               .055                .08627

10                               .055                .07840

9                                 .063                .09277

8                                 .072                .10775

7.5                              .081                .12753

7                                 .081                .11928

6                                 .092                .13166

5.5                              .108                .16654

5                                 .120                .18679

4.5                              .127                .18855

4                                 .143                .21249

3.5                              .185                .30756

3                                 .185                .26632



Download the FREE Thread Wire Measuring Chart Here.

The chart below lists the Wire Size and Constant for measuring Metric 60° V threads using the 3 wire thread measuring system:

Thread Pitch MM:           Wire Size (Inch):        Constant (Millimeters):

.5                                .018 (.4572 mm)         .93859

.6                                .018 (.4572 mm)         .85198

.7                                .018 (.4572 mm)         .76538

.75                              .024 (.6096 mm)         1.17928

.8                                .024 (.6096 mm)         1.13598

1.0                              .029 (.7366 mm)          1.34377

1.25                            .032 (.8128 mm)          1.35586

1.5                              .040 (1.016 mm)          1.74896

1.75                            .040 (1.016 mm)          1.53245

2.0                              .045 (1.143 mm)          1.69694

2.5                              .063 (1.6002 mm)         2.63553

3.0                              .072 (1.8288 mm)         2.88831

3.5                              .081 (2.0574 mm)         3.14110

4.0                              .092 (2.3368 mm)         3.54628

4.5                              .108 (2.7432 mm)         4.33247

5.0                              .120 (3.048 mm)           4.81335

5.5                              .127 (3.2258 mm)         4.91424

6.0                              .143 (3.6322 mm)         5.70042

8.0                              .185 (4.699 mm)           7.16876


Download the FREE Thread Wire Measuring Chart Here.

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For ACME Thread 3 Wire Measuring Click Here

For Metric 30° Trapezoidal Threads 3 Wire Measuring Click Here

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