How to distinguish very thin long screws are fine thread or coarse thread?

Sometimes we will see that M2*0.4 and M2*0.25 are written on the drawings of very thin long screws. What does this mean? Is it concerned with coarse thread fine thread, how should distinguish?

M2*0.4 refers to the thread diameter of the very thin long screws M2, 0.4 refers to the pitch of the thread. Similarly, M2*0.25 is the same meaning, 0.25 is the pitch of the thread. These two different pitch points indicate an M2*0.4 coarse thread, while M2*0.25 is a fine thread.

A coarse thread is a standard thread. In the case that the customer has no special instructions, the screw manufacturer generally defaults that the screw is a coarse thread. And the fine thread is to compare with coarse thread, the pitch of the thread is smaller, more convenient self-locking, anti-loose, the TPI of the thread will be more than coarse thread, can reduce the effect of leakage, achieve the effect of sealing.

From the appearance, the same specifications of the very thin long screws, between them the thread pitch, TPI is not the same. The coarse thread will have more pitch and fewer threads than thin ones. Fine thread, on the other hand, tends to have a smaller pitch, more TPI, and denser thread. It can also be distinguished on the thread marking on the drawing. In general, if it is a coarse thread, they will not be marked on the drawing, but if it is a thin thread, they will be marked on the drawing.