Question

What is the correct way to write pitch diameter combination of thread size 20mm and pitch 2.5mm?

(a) M 20:2.5

(b) M {20,2.5}

(c) M 20×2.5

(d) M 20-2.5

This question was addressed to me during an interview.

Enquiry is from Diameter and Pitch Combinations topic in chapter Metrology of Screw Thread, Gauges for ISO Metric Screw Threads of Engineering Metrology

Answer 1

Right choice is (c) M 20×2.5

To elaborate: While the designation of pitch diameter combination of screw thread, letter M is followed by the values of the nominal thread diameter and the pitch, (in mm) the two being separated by the sign ‘x’. Hence, combination of thread size 20mm and pitch 2.5mm is shown by M 20×2.5.