Abstract: An apparatus (e.g., tube sheet) includes a plate piece, a sleeve piece, and a tube piece. The plate piece defines a hole. The sleeve piece has first and second ends; the second end is shaped to fit through the hole for attachment of the sleeve piece to the plate piece. The tube piece also has first and second ends. Inner and outer cross-sectional geometries of the tube piece and the sleeve piece (e.g., in the case of round tubes, inner and outer diameters) are shaped for the first end of the tube piece to fit in the first end of the sleeve piece and to form a continuous interior fluid flow path from the second end of the tube piece through the plate piece when the sleeve piece is disposed in the hole and attached to the plate piece and the tube piece is disposed in the sleeve piece.