I'm restoring a 1955 Studebaker President and it has an electric component I also seen in other 50's cars, but don't know what is it for. It is similar to this stuff, right now it is disconnected...
So what's its purpose? How is it called?
Looks like a 3 terminal relay (or isolation solenoid). The metal frame is Ground. The large lugs are Battery IN, Battery OUT and the small lug is for RUN or possibly CRANK.
This is a universal heavy-duty solenoid, used for starters and other low-voltage, high-amperage applications.(*)
Manufacturers include Grote, Cole-Hersee, and Standard Motor Products.
The solenoid in your Studebaker probably was used for the starter at one time, and if it's disconnected now it can be removed.
This is beyond the question, but note these types of heavy-duty solenoids are generally not safe for electronics, and a flyback diode must be used on the coil circuit (unless a diode is specifically built into the solenoid).(*)
*Source: firsthand fleet experience.