Unified National Coarse (UNC)

Unified National Coarse (UNC) is the coarse-pitch thread series within the Unified Thread Standard (UTS) for inch-based fasteners. A UNC designation lists the nominal diameter and the coarse threads per inch (TPI) for that size, such as 1/4-20 UNC or 3/8-16 UNC. Compared to fine-thread series, UNC has fewer threads per inch, meaning the threads are more widely spaced.

UNC is widely used for general-purpose fastening because it is typically easier to start and less prone to cross-threading, especially in field assembly or when parts may be dirty, coated, or slightly damaged. Coarse threads also tend to perform well in softer materials (like aluminum, plastics, and wood) because the deeper thread form provides robust engagement. While fine threads can offer better adjustability and sometimes improved resistance to loosening, UNC is often the default choice when you want reliable assembly, good durability, and broad availability across bolts, nuts, and tapped-hole hardware.