Question

$Fig.BasicProfileofISOmetricscrewthread$

The best wire size for measuring effective diameter of an ISO metric thread of 20 mm diameter, using three wire method is __________mm.

• A. 1.543
• B. 1.154
• C. 2.452
• D. 1.425

Answer 1

The correct option is B 1.154



$\frac{\text{P}}{4}=0.5$

$\frac{\text{P}}{2}=1\text{mm}$

$\text{d}=\frac{\text{P}}{2}\sec \frac{\alpha }{2}$

$\text{d}=1\sec \frac{{60}^{\circ }}{2}=\frac{1}{\cos {30}^{\circ }}=1.154$