Question 1

When should I use fine pitch instead of coarse pitch?

Accepted Answer

Use fine pitch when: (1) the joint is subject to vibration and must resist loosening (e.g., automotive axle nuts), (2) fine adjustment is needed (e.g., micrometers, precision fixtures), (3) wall thickness is limited and fewer deep threads are better, or (4) higher tensile strength per thread is required. Coarse pitch is preferred for general assembly due to faster installation and greater tolerance to damaged threads.

Question 2

What is the recommended thread engagement length?

Accepted Answer

For steel-into-steel, 1.0× to 1.5× the nominal diameter provides full thread strength. For aluminum or cast iron tapped holes, use 1.5× to 2.0× diameter. Beyond 1.5D in steel, adding more threads provides negligible additional strength because the bolt shank will fail before the threads strip.