If the cutout dimensions are not the correct measurements indicated, the commercial drop hand sink will either not fit into the countertop, or it will fall completely through. Either outcome is highly undesirable. It is suggested that you use a professional plumber to do the installation and install the drain and water hookups for the commercial drop sink. The faucet center indicates how far apart the water supply lines need to be (either four or eight inches). Most drop-in hand sinks come with a faucet included, but you will want to double check. If the faucet is not included, be sure you select one with the same faucet center as the hand sink. The drain opening diameter tells you how large the drain line needs to be; standard drain pipes are either 1 ½” or 2” in diameter.