Sparta was a limited, economy line of tools made by New Britain and sold only through Napa. Napa owned the Sparta trademark.
When I worked for Napa during the late 70's, Sparta was marketed to the DIY market, while New Britain tools were marketed to professional mechanics. I still have a few Sparta wrenches, and I believe one socket set, that I bought with the employee discount during the ~ 2 years I worked for Napa as a driver/parts drone.