Unified National Standard

Written by Matt Milbury. Posted in Thread Datasheets

Unified National Standard (UNS) replaced American National Standard (ANS)

  • UN replaced N
  • UNS replaced NS
  • UNC replaced NC
  • UNF replaced NF
  • UNEF replaced NEF
  • 1A, 1B replaced Class 1
  • 2A, 2B replaced Class 2
  • 3A, 3B replaced Class 3
  • Class 4 obsolete
  • Class 5 used for interference threads

Tolerance Classes

Classes 1A and 1B

  • This class has the loosest fit.

Classes 2A and 2B

  • This is the most common thread class and used for commercial products. This class is the typical fit.

Classes 2AG

  • This class threads are loose enough to allow for expansion due to high temperatures or even the insertion of a lubricant into the threads. The G is for coated threads so they will not exceed the thread tolerance.

Classes 3A and 3B

  • This is the most precise fitting thread, a very close and tight fit.