Bolts are usually classified in terms of two types of measurements: the metric system and the imperial system. In calipers, the metric system is in units of millimeters, while the imperial system is in units of inches. For example, when a bolt is sized as 12 × 1.25 in the metric system, that means the bolt thread diameter measures 12 mm, and the thread pitch measures 1.25 mm.
So, if your metric bolt measures 0.78 over the threads, that means that the
size of the bolt is 0.78 mm in thread pitch. The attached picture shows how you measure the thread pitch.
Π=180⁰
-7π/2=(-7*180)/2=-7*90=-630⁰
-7π/2= -630⁰
The rate of change is x2. So, since it's forty, it became 80 because 40x2=80!
Good luck for a good grade!