Model 625-9, 4".
Serial Number DBU33XX.
Do you have the box?
The big white box end label is applied right when the box is sealed for shipment, and it has a 4-digit code after the serial number. This is a date code; the first number is the last digit of the year, and the next 3 numbers represent the day of the year numbered consecutively.
FWIW my 638 has a DBD prefix and was made in early August of '08.