Tailpiece and Hose Sizes

By West Marine Staff, Last Updated: 4/5/2019

Hose sizes, with few exceptions, are designated by the inside diameter (ID), which is the size of a round rod that the hose can be slipped onto. The outside diameter (OD) of the hose is only important when selecting hose clamps.

In reality, a half-inch pipe doesn’t actually measure a half inch either inside or outside. In our catalog and on our website, we generally list the size designation and often the inside diameter. Use this diagram, together with careful measuring, to help pick out what you need.