UNF (Unified National Fine) threads are an American imperial thread standard known for their fine pitch, which provides increased strength, superior vibration resistance, and tighter tolerances compared to the coarser UNC (Unified National Coarse) threads.
Key Characteristics
Thread Angle: UNF threads, as part of the Unified Thread Standard (UTS), use a symmetrical V-profile with a 60° flank angle, which is the same angle used for modern ISO metric threads.
Designation: They are designated by their nominal major diameter (in inches) followed by the number of Threads Per Inch (TPI). For example, a 1/4"-28 UNF thread has a 1/4-inch diameter and 28 threads per inch.
Pitch: They have a smaller pitch and a higher thread density than UNC threads, meaning more threads per unit of length.
Strength: The finer pitch results in a larger tensile stress area for a given diameter and a greater number of engaged threads, contributing to a stronger connection less prone to loosening under vibration.
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