This item is a compression fitting for use with water cooling products. This fitting is made to fit with 3/8" ID and 5/8" OD tubing. It is made of brass and is colored black to go with any PC build. Providing a reliable and secure connection, this is the perfect choice for fittings in your water loop, especially looking at its low price. It's crucial to have these so the tubes are fitted snugly onto components. Linking your tubes to your components, it provides a clean look to your custom water loop, from beginning to end.