I think it is best to first cover the frame model number and size because on some frames this is stamped in the middle of the other numbers and can be confusing.

Location:

I have seen the frame model and size stamped in two different locations on the frame:

• across the bottom bracket shell (along with the serial number)

• under the chain stay bridge. ( If the serial number was stamped on the dropout then the frame model and size were stamped on the stay bridge.)

Character stamping:

The character stamping into the frame is very uniform. The characters are upright and evenly spaced.

Format on the bottom bracket:

The first frame model numbers were three digits followed by a spacing and one character for the frame size.

Later the frame model number was five digits followed by spacing and one character for the frame size.

Format on the Chain stage bridge:

The frame model number was five digits followed by spacing and the frame size.

The frame size is sometimes one character and other times two digits.

Frame model number observations:

The frame model number on the bottom bracket start in 1976.

This number is not unique to any given frame. A specific frame model number can be found on several frames.

I assume that frames with the same frame model number are the same tubing and design.
Geometries may vary with the size of the frame.

I assume that the a frame model number may be used across more than one Gitane model.

I assume the above ideas because I do not have enough examples to do any serious verification.

Frame size:

When the frame size is two digits, this is the frame size in centimetres.

When the frame size is a single digit, add 50 to get the frame size in centimetres.

When the frame size is a single letter, the letter “A” translates to 10, the letter “C” to 12, etc..
Add 50 to get the frame size in centimetres.