There is no difference between the two. A bolt is a cylinder with an external thread, and a screw is a pointed cylinder with an external thread. Both can be called screws. Fit with a nut for fastening and connecting two parts with through holes. This connection form is called bolt connection. The nut is unscrewed from the bolt, and the two parts can be separated, so the bolt connection is a detachable connection.
Lock nut: superior vibration resistance. Thread when tighten bolts of tooth top thread which affects tightly into the nut 30 ° cant wedge stuck tightly, and applied to wedge on the slope of the normal force and the axis of the bolts into 60 ° Angle, rather than 30 ° Angle, and therefore, tighten locknut is caused by the normal force is greater than the ordinary standard nut, has a great locking ability to resist vibration.