Which statement best describes the difference between UNC and UNF threads?

Which statement best describes the difference between UNC and UNF threads?

• A. UNC is coarse thread; UNF is fine thread
• B. UNC uses metric units; UNF uses imperial units
• C. They are the same
• D. One is external threads and one internal

Answer: (A)

The difference being tested is how tightly the threads are pitched. The Unified National Coarse series has fewer threads per inch, giving a coarser thread, while the Unified National Fine series has more threads per inch, giving a finer thread. That makes the statement that UNC is a coarse thread and UNF is a fine thread the best description of their relationship. It also isn’t about metric versus imperial (both use imperial units), nor about external versus internal (both can be either). In practice, coarse threads are quicker to assemble and tolerate dirt better, while fine threads provide more holding power and precise adjustment.

The difference being tested is how tightly the threads are pitched. The Unified National Coarse series has fewer threads per inch, giving a coarser thread, while the Unified National Fine series has more threads per inch, giving a finer thread. That makes the statement that UNC is a coarse thread and UNF is a fine thread the best description of their relationship. It also isn’t about metric versus imperial (both use imperial units), nor about external versus internal (both can be either). In practice, coarse threads are quicker to assemble and tolerate dirt better, while fine threads provide more holding power and precise adjustment.