1. What is UN Thread Major Diameter?

The UN (Unified National) thread major diameter is the largest diameter of an external thread, measured at the crests. It's calculated by subtracting the allowance from the basic major diameter.

2. How Does the Calculator Work?

The calculator uses the UN thread major diameter formula:

Where:

• Basic Major — The nominal major diameter of the thread
• Allowance — The intentional difference between maximum material limits of mating parts

Explanation: The allowance accounts for manufacturing tolerances and ensures proper fit between mating threads.

3. Importance of Major Diameter Calculation

Details: Accurate major diameter calculation is crucial for proper thread fit, strength, and interchangeability in mechanical assemblies.

4. Using the Calculator

Tips: Enter basic major diameter and allowance in inches. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between major diameter and nominal diameter?
A: Nominal diameter is the designation size (e.g., 1/4"), while major diameter is the actual measured largest diameter.

Q2: How does allowance differ from tolerance?
A: Allowance is the intentional clearance, while tolerance is the permissible variation in size.

Q3: What are typical allowance values for UN threads?
A: Allowance varies by thread class (1A, 2A, 3A) and size, typically ranging from 0.001" to 0.005".

Q4: Can this calculator be used for metric threads?
A: No, this is specifically for UN threads. Metric threads use different standards.

Q5: How does pitch diameter relate to major diameter?
A: Pitch diameter is the theoretical diameter where thread width equals space width, always smaller than major diameter.