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Fastener Wikipedia-What means of UN、UNR、UNC、UNF、UNS Thread

What means of UNC Thread？

UNC Thread is a part of the Unified Thread Standard (UTS). The Unified Thread Standard (UTS) defines a standard thread form and series, along with allowances, tolerances, and designationsIt is widely used in USA and America Country.

Origin:

Unified Screw Threads is originated by the United States, Canada, and UK in 1949. To replace the American National Standard series and British Standard Whitworth.

Types:

UN：A flat root contour is specified ,but it is necessary to provide for some threading tool crest wear, hence a rounded root contour cleared beyond the 0.25p flat width of the Basic Profile is optional.
UNR：In order to reduce the rate of threading tool crest wear and to improve fatigue strength of a flat root thread, the Design Profile of the UNR thread has a non-reversing continuous curved root tangent to the thread flanks at a depth of 0.625 H.
UNC：Coarse-Thread Series
UNF：Fine-Thread Series
UNEF：Extra-Fine-Thread Series
UNS：Selected Combinations and Other Threads of Special Diameters, Pitches, and Lengths of Engagement
Constant Pitch Series： such us 8UN,12UN,16UN etc.

UNF VS UNC Thread

UNC VS UNF Thread

Marks :

Thread diameter - Number of threads per inch code - Precision grade

For example: Coarse thread series 3/8—16 UNC—2A

Diameter is 3/8 ，16 threads in one inch and Rrecision Grade is 2A

Thread precision Class:

Thread fit refers to the degree of looseness or tightness between mated threads. The grade of fit is the specified combination of deviations and tolerances acting on internal and external threads.

For unified British standard threads, there are three grades of external threads: 1A, 2A, and 3A, and three grades of internal threads:

All Class 1B, 2B and 3B are clearance fits. The higher the grade number, the tighter the fit. In British standard threads, tolerances are only specified for grades 1A and 2A, with grade 3A having zero tolerance. Moreover, the grade tolerances for 1A and 2A are equal.

1. Grades 1A and 1B, very loose tolerance classes, are suitable for the allowance fit of internal and external threads.

2. Grades 2A and 2B are the most commonly used thread tolerance classes in the British standard series of mechanical fasteners.Class

3. Grades 3A and 3B form the tightest fit when mated, suitable for fasteners with tight tolerances, and are used in critical safety designs.

4. For external threads, grades 1A and 2A have a fit tolerance, while grade 3A does not. The tolerance of grade 1A is 50% larger than that of grade 2A and 75% larger than that of grade 3A. For internal threads, the tolerance of grade 2B is 30% larger than that of grade 2A. Grade 1B is 50% larger than grade 2B and 75% larger than grade 3B.