ISO Metric Thread Pitch Diameter Calculator

What Is a Pitch Diameter Calculator?

A pitch diameter calculator finds basic, maximum, and minimum pitch diameters for ISO metric 60° threads. Pitch diameter is where thread thickness equals the gap between threads. It is critical for bolt and nut fit checks in machining and inspection.

Pitch Diameter Formulas

Basic pitch diameter from major diameter $d$ and pitch $P$:

$$d_2 = d - 0.6495 \times P$$

For external threads:

$$d_{2\text{max}} = d_2 + es \qquad d_{2\text{min}} = d_2 + es - T_{d2}$$

For internal threads:

$$D_{2\text{max}} = D_2 + EI + T_{D2} \qquad D_{2\text{min}} = D_2 + EI$$

Tolerance $T$ depends on grade and major diameter. For sheet metal bending, see the K Factor Calculator.

Frequently Asked Questions

What is pitch diameter on a thread?

Pitch diameter is the imaginary cylinder where thread ridge width equals the space between ridges. It controls how tightly a bolt mates with a nut.

Does this calculator work for imperial threads?

No. This tool applies ISO metric 60° thread standards only. UNC, UNF, and other inch-series threads use different tolerance tables.

What does tolerance class 6g mean?

6g is a common external thread tolerance. The number 6 is the grade controlling pitch diameter tolerance. The letter g is the position controlling fundamental deviation.

How do I find pitch diameter of an M25 x 1.5 bolt?

Basic pitch diameter is $25 - 0.6495 \times 1.5 = 24.026$ mm before applying tolerance position and grade limits.

What are pitch diameter limits?

Limits are the maximum and minimum allowed pitch diameters for a given tolerance class. Parts outside these limits may be too loose or too tight to assemble properly.

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Pitch Diameter Calculator

What Is a Pitch Diameter Calculator?

Pitch Diameter Formulas

Frequently Asked Questions

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