Pitch Diameter Formula:
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The pitch diameter (PD) is the diameter of an imaginary cylinder that passes through the threads where the width of the thread and the space between threads are equal. It's a fundamental measurement in thread design and manufacturing.
The calculator uses the pitch diameter formula:
Where:
Explanation: The formula accounts for the relationship between major diameter, thread pitch, and the theoretical perfect fit between mating threads.
Details: Pitch diameter is crucial for determining thread fit class, calculating thread strength, and ensuring proper thread engagement in bolted joints.
Tips: Enter major diameter in inches and threads per inch. Both values must be positive numbers. For standard thread sizes, consult engineering references for exact dimensions.
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 theoretical diameter where thread width equals space width.
Q2: How accurate is this calculation?
A: This provides a theoretical value. Actual manufactured threads may vary slightly due to tolerances and manufacturing processes.
Q3: Does this work for metric threads?
A: No, this formula is for imperial threads. Metric threads use pitch (distance between threads) rather than TPI.
Q4: What is the 0.6495 constant in the formula?
A: It's derived from the geometry of the 60° thread form (UN/ISO standard) where the height of the fundamental triangle is 0.866025p and pitch diameter occurs at 0.75 times this height.
Q5: When would I need to calculate pitch diameter?
A: When designing custom threads, checking thread gauges, or calculating thread strength and fit classes.