A tray includes a plurality of rows, each of which includes a plurality of slots. Each row contains a plurality of screws. Different rows may contain screws of different types, e.g., lengths. Each of one or more rows contains a machine-readable object (e.g., peg) containing data representing properties of the objects in the corresponding rows. Removal of an object from a row is performed by reading data from the machine-readable object in the row and using that data to modify (e.g., decrement or increment) a count of the type of object contained in that row.