A guide to UNC thread gage and its use

A guide to UNC thread gage and its use

Mar 1, 2019, 7:12:52 PM Tech and Science

A thread gauge is a device used for measurement. It is used for different purposes like measurement of the angle of thread, pitch, measurements of screw threads and its diameter, etc. This device is not used as a tool of precision. Rather, it is used to know the shape and size of the pitch or the thread. This device is mostly used to save time as it removes the manual job of measuring the thread or the thread pitch. There are many types of thread gauges. Likewise, there are many types of symbols of thread gages also.

What are UNC thread gages?

UNC thread gages stand for Unified National Coarse thread gage. It generally has an angle of 60 degrees. The thread gages of unified series are available in four types. They are UNC, UNF, specials and UNEF.

What is the history of these thread specifications?

The UTS or Unified Thread Standard defines a standard for the form and series of the thread. It also includes allowances, designations and tolerances for screw threads. It also acts as a primary standard for nuts, bolts and a wide range of tools termed as thread fasteners. All these tools possess a standard degree of 60 just like the ISO metric thread. But the difference from the ISO metric thread is in the characteristic dimension. In UTS thread the characteristic dimension that is the outer diameter and the pitch is in inch fraction and not in millimeter value. The UTS was accepted by the United States of America, Canada and Great Britain in the year 1949. Over the years, the specifications have undergone many changes as per the developments.

What are the other symbols or designations in the Unified Thread Standard along with UNC thread gages?

The UTS is classified into three types of threads. They are fine threads, extra fine threads and coarse threads. There are three more symbols in UTS along with UNC thread gages. They are;

UNF: A symbol which stands for Unified Fine pitch threads,

UNS: A symbol which stands for Unified Special threads.

UNEF: A symbol which stands for Unified Extra Fine pitch threads.

What are the different types of Unified Threads?

The most used UTS designations are UNF and UNC. The threads used for these unified symbols change according to the requirements.  The threads used for these designations are divided into three different types. They are:

1A (external) and 1B-(internal) - This type of thread is used when a good amount of tolerance is required for easy assembly. Even when the thread is nicked or slightly cut, the amount of tolerance required does not change.

2A (external) and 2B (internal) - This type of thread is most popular for its use. This type is mostly used for all general applications and hence is the popularity.

3A (external) and 3B (internal) - This type is used when the accuracy of the thread plays a very important role while measuring. And when the closeness of fit plays an important role, then this thread is mostly used.

Published by Rosie Joy

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