The difference UNC UNF UNEF UN

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The difference UNC UNF UNEF UN

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The Unified National Thread Series (UN) is a system of thread standards used in the United States. Within this system, there are several different types of threads, each with its own specific features and applications.

First, there is the Unified National Coarse (UNC) thread, which is the most commonly used thread in the US. This thread is identified by its relatively large thread pitch and is used for fastening applications where strength is a primary concern.

Second, there is the Unified National Fine (UNF) thread, which is commonly used in applications that require finer thread pitches and greater resistance to vibration. This thread is often used in aerospace and automotive applications.

Third, there is the Unified National Extra Fine (UNEF) thread, which is similar to the UNF thread but has an even finer thread pitch. This thread is used for applications where precision is critical, such as in instrumentation and control systems.

Finally, there is the Unified thread, which is a combination of the UNC and UNF threads. It is used in applications where flexibility is desired, such as in general-purpose fastening applications.

Overall, the UN thread series offers a range of options for fastening solutions, from high-strength applications to those requiring precision and flexibility. By understanding the different types of threads available within this system, engineers and manufacturers can select the right thread for the job and ensure successful and efficient production.

Selection of diameter/pitch combinations
Standard diameter/pitch combinations which are given in Table 1. Having regard to the information in Clauses 4 to 7 and to BS 35804), choice should preferably be made first from the UNC or UNF series. If these are unsuitable, choice should be made from the UNEF or the constant pitch series. Of the latter, preference should be given wherever possible to the 8 UN, 12 UN, 16 UN and 20 UN series. When selecting from the constant pitch series, an endeavour should be made to choose a first choice diameter. If no first choice diameter is suitable, a second choice diameter should be used.

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