1. What is UN Thread Pitch Diameter?

The UN (Unified National) thread pitch diameter is the diameter of an imaginary cylinder that passes through the threads where the thread width equals the space between threads. It's a fundamental measurement for thread design and inspection.

2. How Does the Calculator Work?

The calculator uses the standard UN thread formula:

Where:

• Major Diameter — Largest diameter of the thread (inches)
• TPI — Threads per inch
• 0.6495 — Constant for UN thread form

Explanation: The formula accounts for the standard 60° thread angle and 1/8 pitch truncation of UN threads.

3. Importance of Pitch Diameter

Details: Pitch diameter determines thread fit and strength. It's critical for proper thread engagement and is often measured with thread micrometers or three-wire method.

4. Using the Calculator

Tips: Enter major diameter in inches and TPI (threads per inch). 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 and space widths are equal.

Q2: Does this work for all UN thread series?
A: Yes, it works for UNC (coarse), UNF (fine), UNEF (extra fine), and UNS (special) threads.

Q3: How accurate is this calculation?
A: It provides theoretical values. Actual measurements may vary due to manufacturing tolerances and wear.

Q4: Can I use this for metric threads?
A: No, metric threads use different constants. Use ISO metric thread formulas for metric threads.

Q5: What about thread class of fit?
A: This calculates basic pitch diameter. For different classes (1A/1B, 2A/2B, 3A/3B), apply appropriate tolerances.