ACME Thread Measuring - Calibration

An ACME thread has a screw thread profile with trapezoidal outlines and they are commonly used where large loads or high accuracy are required; for example, in a vice or lead screw. The ACME thread has a 29-degree thread angle with a thread height half of the pitch (P/2) and where the apex and valley are flat. An ACME thread profile is typically easier to manufacture than other thread series. This thread form also allows for the use of a split nut, which minimizes nut wear, however, the radial load on the nut is greater thus minimizing efficiency. Similar thread series are the square thread and buttress thread.

Some applicable ACME formulas are:

Pitch diameter: E = M + 1.933357 * P – 4.993929 * W

Best wire size: W (best) = 0.51645 * P



            E = Pitch diameter

            M = Measurement over wires, i.e., the machine readout

            TPI = Threads-per-inch

            P = Pitch (1/TPI)

            W = Calibrated thread wire size


Pratt & Whitney offers these machines suitable for ACME threads:

1.      Labmaster Universal (Models 175, 1000M,1000A)

2.      Laser Measuring Machine

3.      Labmicrometer (Models 900, 1600)

4.      Digital Measuring Machine

5.      Universal Supermicrometer (Model 501, 504)

6.      External Supermicrometer (Model B, C, PC)