There are 3 Models with model number 501 in the database
Small time only clock with blue crackle finish, and etched silver and gold color metal dial.
Dates made: 1928 - August 1929
Small time only clock with blue solid color finish, and etched silver and gold color metal dial.
Dates made: August 1929 - December 1933
Clock of Tomorrow in black case with brass trim. Black luminous dial, single key wind, chime alarm.
Dates made: 1955 - 1959