According to a 1933 Pro-Swing advertisement, "The Pro-Swing principle of balanced weight and spring induces just the right amount of pull on the arms and body to produce smooth rhythm and correctly applied power." 

Produced by the Pro Swing Golf Co, Inc. of New York City, Pro-Swing practice clubs were marketed as the cure for any number of faults and the teacher for golfers of any level.  "It makes you swing correctly. It compels you to drag back the clubhead instead of lifting it too soon.  It compels you to shift your weight correctly.  It compels you to put wrist snap into the shot.  It compels you to follow through." And more.

This example is in solid condition.  A little of the original red paint remains on the spring, which is straight. The grip is original. The weight is the lead ball, which still has traces of its gold paint.