BXXX is a style reference. See the Current Bracelet Designs for examples of other styles.
SNXXXXX is the serial number of a specific piece of jewelry. Not all pieces have a serial number as applying it might damage the piece.
B034 SN20016 is a size 53 which means that it will fit a wrist that is approximately 6.75" in circumference depending on whether or not you like a cuff bracelet to be tight or loose.
If SN20016 is not your size, B034 is a Current Design and a new bracelet can be made to fit your wrist. This will require that you contact me by phone or email.