Screw thread stands for a incessant helical groove of specific cross-section that is created on the external or internal surface. If a screw thread is developed on a cylinder, it is called as straight or parallel screw thread, whereas screw thread developed on a cone or frustum is called as the tapered screw thread.
Application of screw threads :-
1. To retain parts jointly 2. To modify the parts with respect to each other. 3. To transfer power
Given below, some vital components of screw threads :-
Root Bottom part of the thread where both sides intersect.
Crest Top part of the thread where both sides intersect.
Flank It refers to the straight sides which attach the crest with root.
Thread Angle Angle at which both sides of the thread intersect.
Axis of a screw Longitudinal centerline via a screw
Base of the thread, Bottom section of the thread., Highest section among the two adjoining roots.
Depth of thread Space from crest to root computed vertically.
Lead Distance covered by a nut in one complete revolution. Single start threads – Lead = Pitch Multi start threads – Lead = Pitch x number of starts.
Threads per inch Number of threads in one inch. Length of screw. It is called TPI in short form.
Thickness of threads Space among the adjoining sides of the threads computed along the pitch line.
Depth of engagement Depth of the thread in contact of two mating parts calculated radically.
Length of engagement Length of contact among two mating parts calculated axially.