1. What is Pitch Diameter?

The pitch diameter (PD) is the diameter of an imaginary cylinder that passes through threads at the point where the width of the thread and groove are equal. It's a critical dimension for thread design and measurement.

2. How Does the Calculator Work?

The calculator uses the metric pitch diameter formula:

Where:

• \( PD \) — Pitch diameter (mm)
• \( D \) — Major diameter (mm)
• \( P \) — Pitch (mm)

Explanation: The formula accounts for the relationship between major diameter and pitch in metric threads.

3. Importance of Pitch Diameter

Details: Pitch diameter is essential for determining thread fit, strength, and interchangeability. It's used in thread gauging and quality control.

4. Using the Calculator

Tips: Enter major diameter and pitch in millimeters. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between major and pitch diameter?
A: Major diameter is the largest diameter of the thread, while pitch diameter is the effective diameter where thread contact occurs.

Q2: Does this formula work for all thread types?
A: This specific formula is for metric (ISO) threads. Other thread types (UN, Whitworth, etc.) have different formulas.

Q3: Why is the constant 0.6495 used?
A: This constant comes from the geometry of standard metric threads (60° thread angle) where H = (√3/2)P ≈ 0.866P, and PD = D - (3H/4) = D - 0.6495P.

Q4: How accurate is this calculation?
A: The formula provides theoretical values. Actual manufactured threads may have tolerances and variations.

Q5: When would I need to calculate pitch diameter?
A: When designing threaded components, selecting thread gauges, or troubleshooting thread fit issues.