One very crucial edge that the UN thread taps have over others is that it is so easy to deduce the primary thread diameter, the thread per inch alongside the fineness or the coarseness of the thread even without being a pro. The Unified national thread gauge, which is also known as the UN thread tap originated as a result of the problem of interchangeability that was experienced when making use of the other standard of thread taps. This improved standardization came through to be with the joint effort of the United States of America, Great Britain, and Canada. Thou has the years go by; several modifications are being asked to the UN thread taps.
Alongside the various modifications done was the incorporation of the UN thread tap series. There are three common and known UN thread tap series, although it is not limited to these three. The three major ones include:
The fine thread: This Unified national thread is symbolized as the UNF. Its load breaking capacity happens to be higher than that if their coarse counterpart. This reason is as a result of the high tensile stress area that they have for gages having similar material and diameter. They do also have lesser thread depth, unlike the Unified coarse thread gauge. This also contributes to their high load breaking capacity. Fine adjustment is also possible when making use of the Unified national beautiful thread tap because of the smaller lead angle in them.
The coarse thread: Another member of the UN tap series is the Unified national coarse thread, which is symbolized by the UNC. Most operators considered it the best choice for general-purpose gaging. The UNC has deep depths and is commonly used in operations where find threads are not suitable. Their coarse pitch makes it possible for easy assembly without cross-threading.
The extra-fine: commonly known as the UNEF thread, which stands for the Unified national extra fine thread, happens to be the last member of the UN thread tap series. It has almost identical features with the UNF thread gages, although it differs slightly.
Other series in the UN thread tap include the Unified national special, the Unified round, and the Unified constant pitch. These additional members are also very much used in metrology today, and they serve significant purposes.
The Unified national special is symbolized as the UNS. It has the thread pitch inch specified, but there is a limitation to the thread pitch inch for specific diameters.
The Unified constant special is employed in applications where the Unified national fine thread and the Unified national coarse thread are not applicable. This is due to the full range of pitch diameter it possesses.
The Unified round: in this case, the root radius of the Unified series is rounded. Hence it's named, UNR. It is not uncommon to see that most external fasteners manufacturers produce more of the UNR instead of the regular Unified threads.