When I first started in the business, we were issued a B Box. As I remember, it had a B in the serial number or was just labeled with a B. KS-7771 I assume would be an older model. For the tech on the road, these were a perfect place to organize your tools. BUT they were heavy and it was too much weight to carry any distance! Most techs carried a small bag with your most used tools (punch tool, butt set etc) and these were left in there car. This is a nice piece....Doug