Types of vee threads

 VEE THREADS

.types of 'vee' threads used for thread fastening

. distinguish the features of different 'vee' thread forms

. designate different types of 'vee ' threads

Types of 'vee' Threads

'Vee' threads are available in different forms and standards. The type of ' vee' threads used for general engineering threaded fasteners are

ISO metric thread

ISO inch(unified thread)

British standard whitworth thread

British standard fine thread.

ISO metric thread

This is the form of thread approved by B.I.S. for threaded fastening. Two series of threads have been identified by them. They are

ISO meric-coarse

ISO metric-fine.

The thread angle is 60°.the root of the external thread is rounded. The crest of the external thread is flat, but sometimes it is rounded depending on the type of the manufacturing process. The root of the internal thread is cleared beyond the width equal to one eighth of the pitch and is rounded. The Crest of the internal thread is left flat.

Designation of ISO metric thread

ISO metric coarse thread is designated such as M12 and M12×1.25

Example -M12

The symbol M indicates that it is ISO metric thread and 12 is  the diameter of the thread. For the coarse series the pitch of the threads is standardized for each diameter.

ISO metric fine the threads are designed as

Example M12×1.25

The addition of 1.25 in the case indicates the pitch of the thread.

ISO Inch(unified)thread

The ISO inch system (unified) is a recognized standard for interchangeability with the American National Thread.

These threads are used for general purpose engineering threaded fastening and are of two types.

Unified coarse(UNC)

Unified Fine(UNF)

For unified threads the Angle is 60°.The thread profile is similar to that of the ISO metric thread.

Designation of ISO inch(unified )threads

Example -a)1/4 20 UNC

                   b)1/4 28 UNF

Example (a) indicates that the diameter of the thread is 1/4",it has 20 threads per inch (TPI) and the ISO thread series is UNC(unified coarse). Example (b) has 28  TPI and is of UNF series.

British standard whitworth (BSW) thread

This thread is being replaced by ISO metric thread. However, the application of the thread is still being continued in a limited manner, particularly in the production of spare parts and repair works. These threads have 55° angle and are rounded at the crest and the root. There are a definite number of threads per inch for a particular diameter.

These threads are designated by the diameter in inches followed by the abbreviation of thread series.

Example -1/2BSW

British standard fine(BSF) thread

This thread has the same form as BSW, but with finer pitches.

The threads are designed by the diameter in inches followed by the thread series.

Example -3/8" BSF