This is the most common diameter of plumbing in North America. It has been the standard size used by plumbers for 40 years. Changes are this will adapt perfectly under your sink. When measuring the plumbing under your sink, you need to measure the diameter of the plumbing like and not the OD (outer Diameter) or ID (Inner Diameter) of the plumbing threads under your sink. The Plumbing adaptor is 3/8" x 3/8" x 1/4". This enables you hook up your system to you homes cold water line without having to pierce any cold water lines.