For a screw, the angle of helix ($$\alpha$$) is related to the lead (L) and mean screw thread diameter (d) as

A

$$\tan \alpha = \frac{L}{d} $$

B

$$\tan \alpha=\frac{d}{L} $$

C

$$\tan \alpha=\frac{L}{\pi d} $$

D

$$\tan \alpha=\frac{\pi d}{L} $$