Thread Types and Standards

In this compact blog post, we're going to talk about the thread types and standards. Our customers ask our support team from time to time various questions on the subject: “Conversion of a thread and thread standard”, so we hope that this article will be useful for Internet surfers to provide a general understanding in the technical field.

In the first part we will look at the most common imperial and metric standards of the thread. The second part is devoted to the topic of “Conversion in general”. This article can help you to identify the most common connections for refrigeration and air conditioning.

Abbreviations and Standards (SAE, UNF, NPT...)

There are still many different connection systems, developed according to international and national standards and specific markets. This confuses people and brings some chaos to the standardization of the thread. The majority of systems use metric and imperial thread types. The metric thread is determined by the outer diameter and the thread pitch - the distance between two tips of the thread. The inch thread is determined by the outer diameter and the number of threads per inch.

The most common imperial thread types in the world are listed below:

• SAE (Society of Automotive Engineers - US standardization company similar to the VDA, but with the meaning of DIN) - American connection form (metallic sealing screw-in thread). cylindrical UNF thread with O-ring on the sealing collar (cone connections with 45 ° sealing surface UNF thread), widely used in refrigeration and air conditioning systems
• UNF (Unified-National-Thread-Fine) - Fine thread according to US standards with a flank angle of 60 ° (same as the * metric ISO thread) defined by the outer diameter of a screw in inches and the thread pitch in revolutions per inch, used for the most common screws and nuts, also called ISO threads in inch dimensions;
• NPT (National Pipe Taper) - American thread form, conical thread in which the sealing takes place via the thread flanks.

*Metric ISO pipe thread (M thread) similar to Whitworth pipe thread, tapered, cylindrical external thread or cylindrical internal thread, is also known as inch thread.

Below is an example of the thread M14X1,5: