Question

Which of the following are main elements, error in any of these can cause rejection of thread?

(a) Major diameter and minor diameter

(b) Major diameter, minor diameter and effective diameter

(c) Major diameter, minor diameter, effective diameter and pitch

(d) Major diameter, minor diameter, effective diameter, angle of thread and pitch

I have been asked this question during an interview.

My question comes from Effect of Pitch Errors in portion Metrology of Screw Thread, Gauges for ISO Metric Screw Threads of Engineering Metrology

Answer 1

Right choice is (d) Major diameter, minor diameter, effective diameter, angle of thread and pitch

For explanation I would say: In case of plain holes and shafts, there is one dimension only which has to be considered i.e. diameter. Errors in diameter if exceed the permissible tolerance, will result in rejection of part. But in case of screw threads there are minimum 5 important elements which are Major diameter, minor diameter, effective diameter, angle of thread and pitch and error in any one of these will result rejection of the thread.