A.The designation one- or two-piece refers to the pop-up body that attaches the sink to the drain pipe. The 1 piece body has the fitting for the pop-up lever in the part that is installed when the drain flange is installed, thus making the alignment to the pop-up rod more difficult than the 2 piece. The 2 piece body has the fitting for the pop-up lever in a separate part that is installed after the drain flange has been installed, making the alignment with the pop-up rod much easier.