I bought a couple lenses and a camera is coming along - a #7A Century Studio (and stand)

In looking around - I can find 9's and 4's and Masters along with the 7 and 7A


but what I can't find is any information as to what the numbers mean? size? model number (like Nikon F, F2, F3 etc)?


is there someplace to look that up?


it's an 8x10 with 5x7 and 4x5 backs



thanks