Why the screw thread more closely, spin into the more effort?
This is due to the spiral angle of the thread becomes smaller, the pitch of the thread, the lead becomes smaller.
Screw thread more dense, indicating the screw thread deep and shallow, the screw in the advance the resistance of the smaller, when the spin naturally more effort.
Because the length of the screw into a certain, do a certain job. The more tight the thread, the equivalent of the longer the distance rotation, power = distance × force, long distance, the need for force naturally small
