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23 Φεβ 2024 · For example, “#1 – 64” means a #1 size screw with 64 threads per inch. For fractional sizes, it is shown as a fraction followed by the thread count, e.g., “1/4″ – 20” means a quarter-inch diameter with 20 threads per inch.
For example, 1/4-20 means a thread with a pitch of 20 TPI (1/20=0.05″). It is also allowed to denote the pitch by distance. For example, 1/4-0.05P means a thread with a pitch of 0.05″ (same as 20 TPI).
16 Μαΐ 2022 · You'll find a quick reference chart for UNC/UNF - Unified National Threads in this post. If you're new to any of the terminology, scroll down past the chart, and you'll find a list of definitions to help you better.
UNS (unified special thread) is the standard for screws, nuts, bolts, and other threads in the United States and Canada. They possess the same 60° angle between crests and troughs as NPT but are not interchangeable with them. Threads in this series include UNC (coarse), UNF (fine), UNEF (extra fine), and UN (fixed pitch). NPT Thread Size Chart
UNF threads are known for their fine thread pitch, which means the threads are closely spaced, resulting in a tighter fit between the male and female threads. This characteristic allows UNF fasteners to withstand higher tensile loads and makes them less susceptible to loosening under vibration.
When the thread is smaller than 1/4”, the diame-ter is given with a number from No. 0 to No. 12 (No. # x 0.013” + 0.060”). Mostly, the pitch is not written as it is determined of the diameter for UNC, UNF and UNEF threads. If no tolerance class is written, it means that the tolerance is 2A for external threads and 2B for internal.
So, a 1/4-20 screw has a 1/4" diameter (.250") with 20 threads per inch. Sometimes the terms “coarse” (or UNC/Unified Coarse Thread) or “fine” (UNF/Unified Fine Thread) are used to describe the thread. The term does not refer to the quality of the thread but rather to the frequency of threads per inch.
