The angle of I.S. thread (V shaped) is :

British Association threads

This thread has an included angle of 47 1/2°. Depth and other elements are as shown in the figure. It is used in small screws of electrical appliances, watch screws, screws of scientific apparatus.

Acme threads

Acme threads are used in lathe lead screws. This form of thread enables the easy engagement of the half nut. The metric acme thread has an included angle of 30°.

All of the above

The reasons for rough and broken threads are
Thread cutting tool is blunt
The size of hole or diameter of the blank for bolt is not correct
The flutes of cutting tool are filled with chips

Pitch of thread

The distance between one point on a screw thread and the corresponding point on the next thread, measured parallel to the axis is called as Pitch of Thread.