TABLE OF CONTENTS Screw threads are important elements of mechanical design with wide and varied applications, particularly for controlled translational motion and for fasteners providing disengageable connections.
Screw threads are composite design elements that, distinguished from, for example, a cylindrical shaft or hole, are defined by specific form and dimensional parameters, several of these being considered as principal and the others as complementary. The principal parameters determine the basic functional properties of the screw thread, such as whether it can be assembled with a mating part, whereas the complementary parameters affect the service performance of the threaded machine components.
Threaded components operate in conjunction with a mating member, which is also a threaded machine element, such as a nut fitting a screw. Occasionally, in particular mechanical designs, the mating member may contain only skeleton elements of the complete screw thread deemed sufficient to support and guide the fastening or translating functions of the completely threaded member. In other designs the mating members of the threaded couple are not in direct contact with each other, but operate by means of intermediate transfer elements, such as in the case of ball screws.
The basic shapes of threaded mechanical elements are those of a cylindrical shaft and a cylindrical hole, except in the case of taper threads, such as used for pipes and fittings. Consequently, screw threads are produced equally on external and internal surfaces, a characteristic that affects both their production and measurement.
As in all other mechanical elements, the actual sizes of...
