Knowing how tubing and quick fitting are sized is very important. There are two main sizing types when dealing with plastic tubing, and they are very different. Smaller diameter fittings, that are measured by outer diameter (OD), are specifically designed for use with LLDPE type tubing, or low linear density polyethylene. The larger fittings, in half-inch, three-quarter inch, one inch, and above are considered CTS, or copper tube size, fittings. CTS fittings are made to be compatible with PEX tubing, which is a polyethylene-type tubing. These fittings are made in very specific measurement classes. So, a 3/8 CTS fitting is not going to work in an application that requires a 3/8 OD fitting.

Most fittings are rated to work on copper tubing as well, but it is not the best kind of tubing to use with OD and CTS fittings. If you want to use copper or stainless steel tubing, it is best to look for fittings made specifically for those types of applications. John Guest is one of these manufacturers that makes compatible fittings with stainless-steel. They call them the super-seal fittings.

There is a lot to know when it comes to quick-connect fittings. Every manufacturer chooses to build, size, and shape their fittings differently. Once you have a basic understanding of what a quick-connect fitting is and whether or not you need them, then browse the different brands that Fresh Water Systems offers so you can decide which kind of quick-connect fitting is right for you.

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