1. What is Screw Thread Load?

The screw thread load (F) is the force that can be withstood by the threads of a screw or bolt before failure occurs. It depends on the shear stress (τ) and the thread shear area (A_th).

2. How Does the Calculator Work?

The calculator uses the screw thread load equation:

Where:

• \( F \) — Screw thread load (lb)
• \( \tau \) — Shear stress (psi)
• \( A_{th} \) — Thread shear area (in²)

Explanation: The equation calculates the maximum load that can be applied to a screw thread before shear failure occurs.

3. Importance of Thread Load Calculation

Details: Proper thread load calculation is essential for ensuring mechanical fasteners can withstand applied forces without failure, critical in structural and mechanical design.

4. Using the Calculator

Tips: Enter shear stress in psi and thread shear area in in². Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: How is thread shear area determined?
A: Thread shear area depends on thread geometry and can be calculated from thread standards or measured experimentally.

Q2: What are typical shear stress values for common materials?
A: Steel screws typically have shear stress values between 30,000-60,000 psi, while aluminum may be 10,000-30,000 psi.

Q3: Does thread pitch affect the load capacity?
A: Yes, finer threads generally have smaller shear areas and thus lower load capacities than coarse threads of the same diameter.

Q4: Should safety factors be applied to these calculations?
A: Yes, engineering practice typically applies safety factors of 2-5x depending on application criticality.

Q5: How does thread engagement length affect load capacity?
A: Longer engagement increases shear area proportionally, but only up to about 1.5 times the bolt diameter where full strength is achieved.