Unified Threads - Imperial

The Unified Thread System (or Unified Thread Standard - UTS) defines a standard thread form and series - along with allowances, tolerances, and designations - for screw and bolt threads commonly used in the United States and Canada.

Unified form threads are designated by abbreviations such as U.N.C. (unified coarse), U.N.F. (unified fine), U.N.E.F. (unified extra fine), U.N.S. (unified special, and U.N. (unified constant pitch), with the thread major diameter preceding the designation. For example, 1/4" UNF or 3/8" UNC. 

U.N.C

Is the most common thread type of the Unified Thread System (U.N.C. - U.N.F. - U.N.S. - etc.) and is the preferred thread type for general purpose inch fasteners. Because of the coarse pitch, the threads are deeper than fine threads (U.N.F.) and are easier to assemble with far less cross-threading.

U.N.F.

Is a thread type of the Unified Thread System (U.N.C. - U.N.F. - U.N.S. - etc.) that has a slightly higher breaking load capacity than U.N.C. (Unified National Coarse) threads. This higher breaking load capacity is a result of the more shallow thread depth and larger tensile stress area for fasteners of the same identical material and diameter. The smaller lead angle allows for fine adjustments where needed.