Compression fittings are the largest grouping of fittings. Most of the fittings consist of a nut, a sleeve (or ferrule), and body. Not all of the fittings are compression on every end. Some contain pipe thread as well as compression.

Other options may be available but not common.

Compression fittings are popular because they do not require soldering, sealants such as joint compound (pipe “dope”) or thread seal tape.

Let us first take a look at the sleeve. There are several different types of sleeves, all compression but not intended for the same purpose. For now are concerned with the common sleeve. The sleeve is rounded on the outside and should seat within the curved contour of the body as well as the nut. The sleeve is fairly sensitive and should not be loose allowing it to be “dinged”.

The most confusing thing about compression fittings is when the nut has come off. Is it pipe or is it compression? Well, first the thread size and nominal measurements are not the same. Secondly, as a general guide, a compression end should have a slight curvature to allow the sleeve to seat properly and pipe ends commonly just end.

Compression Thread Chart

For this series of compression fittings there are two types of compression nuts. Standard fittings use short nuts. Long nuts are available for higher vibration applications.