There are several standards used for internal nipple shape and sizing. Contact the wheel manufacturer for the most up to date sizing information.
SW-15: three sizes in one wrench. 3.2mm square socket, 5mm hex socket, 5.5mm hex socket.
SW-16: 3.2mm square socket
SW-16.3: 3/16" hex socket (4.76mm)
SW-17: 5mm hex socket
SW-18: 5.5mm hex socket
SW-19: 6mm hex socket