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What does UNF or UNC refer to with Compressor Oil Filter Threads?

Published by Filter Element Store on Nov 17, 2023

"There is a number on my compressor oil filter followed by the letters UNF. What does UNF and UNC mean and how can I tell them apart?"

UNF and UNC are the two main thread types in the Unified Screw Thread (UST) Standard. UNF stands for Unified Fine Threads and UNC stands for Unified Coarse Threads. 

An oil filter element used with a compressed air system will usually have a threaded connection. Sometimes the oil filter will have two threaded connections. When it comes to selecting an oil filter for your compressed air system, understanding the threading is essential to ensuring compatibility and optimal performance. This becomes even more important when shopping on a website, where you can't check to see if the oil filter thread fits your equipment.

UNF and UNC Explained

A thread on an oil filter, or any other machine part, is often denoted by a measurement followed by a numerical value and the letters UNF or UNC. But what exactly do UNF and UNC signify? These are not just random acronyms; they represent the two principal thread types under the Unified Screw Thread (UST) Standard.

  • UNF (Unified Fine Threads): UNF threads are characterized by their smaller pitch and are generally found in applications requiring higher tensile strength, improved fatigue resistance, and the ability to seal tightly. These are often used in aerospace, precision instruments, and automotive applications.
  • UNC (Unified Coarse Threads): Conversely, UNC threads have a larger pitch and are typically utilized in areas that demand ease of assembly or where rapid, straightforward fastening is necessary. They are commonly found in construction and machinery where fine precision isn’t as critical.

Understanding the nuances of UNF and UNC threads, as well as the application of single or dual-threaded connections, is crucial in selecting the right oil filter for your application. If you're ever unsure of which oil filter is correct for your application, just contact us and we can provide a drawing and specifications so we all stay out of trouble!