Question

What is the formula of virtual effective diameter in case of unified threads?

(a) Simple effective diameter + [ (1.73 x pitch error) + 0.0098 p (θ1 + θ2)].

(b) Simple effective diameter – [ (1.73 x pitch error) + 0.0098 p (θ1 + θ2)].

(c) Simple effective diameter + [ (1.59 x pitch error) + 0.0098 p (θ1 + θ2)].

(d) Simple effective diameter – [ (1.59 x pitch error) + 0.0098 p (θ1 + θ2)].

The question was posed to me by my school teacher while I was bunking the class.

My enquiry is from Effect of Pitch Errors topic in chapter Metrology of Screw Thread, Gauges for ISO Metric Screw Threads of Engineering Metrology

Answer 1

Correct answer is (a) Simple effective diameter + [ (1.73 x pitch error) + 0.0098 p (θ1 + θ2)].

To explain I would say: For unified thread total virtual effective diameter is Simple effective diameter + [ (1.73 x pitch error) + 0.0098 p (θ1 + θ2)] while in case of metric thread it is Simple effective diameter + [ (1.722 x pitch error) + 0.0131 p (θ1 + θ2)].