Abstract: The box has an end wall and four side walls extending therefrom to an open end. The end wall and each of the side walls has a plurality of different size concentric geometric figures formed by grooves in one side thereof whereby the end wall and each of the side walls may be cut along the grooves to form different size openings for receiving different size conduits for the flow of air therethrough. The open end of the box is adapted to be coupled to an inlet formed through the wall of a house or building for use as a register box. A wye connector adapter plate also is provided for connection to the open end of the box whereby the box may be used as a wye connector. The adapter plate has a plurality of different size concentric geometric figures formed by grooves in one side thereof whereby the adapter plate may be cut along the grooves to form different size openings for receiving different size conduits for the flow of air therethrough.