Different forms of screw thread

 Different Forms of Screw Thread

. basic forms of screw thread

. uses of different forms of screw thread

. the features of each form of screw thread

Basic Forms of Screw Thread

Screw threads of different forms are available for meeting the various requirements. The basic forms of screw thread are

Vee thread

Squre thread

Trapezoidal thread

Vee threads

These threads  are of a 'V' shape. Vee threads of different types are available. Vee threads is the most commonly used form of screw threads, and is used for domestic and industrial applications like bolts, nuts and spindles for micrometers etc.

Square threads

The cross section of these threads is square in shape. These threads are very strong, and are used on fly presses, screw jacks, and vice and spindle etc.

Knuckle thread is a modified form of squre thread. In this case the crest and root are rounded to form a semi circle. An example of the use of this thread is the one used for railway wagon coupling.

Trapezoidal Threads

This is also a modified square thread. The angle between the flanks is 30°.

These threads are  also strong and are used for easy engagement and disengagement in transmission. Lead screws of machine tools are made of trapezoidal threads. Acme thread is another type of trapezoidal thread with 29° angle between flanks.

Saw-tooth Thread

This form of thread has an inclination of 3° on one side and 30° on the other sid. These threads are used in places where sliding forces act in one direction.

Spindles of Carpenter's vises and quick release presses have saw-tooth threads. Buttress thread is another thread which is similar to saw-tooth thread. This is read has one flank vertical, and the other at 45°.