Getting the right measurement is the first step to a leak-free installation. Measure the outside diameter of your water neck to determine which AutoPlumb Water Neck Adapter you need. Available in -16AN and -20AN, our patented adapters let you convert your cooling system with no welding, no hose clamps, no splices, and no reducers. Shop at autoplumb.com #restomod #CarEnthusiasts #HotRod #ANFittings #CoolingSystem