Common Eccentric & Gear Nut 95691 wrench

[Wrenchmensch]

I bought this pitted wrench last weekend ($.50).  I hadn't seen one before embossed with "ECCENTRIC & GEAR NUT 95961". The eccentric and gear nut socket opening is 9/16"; the closed end connecting rod screw opening is 15/16".

Who made these wrenches?  Who sold them. What eccentric nut,  on which car, and when?  Is this a very common wrench?

[Bus]

Because of similarity in markings and part number to known Delco wrenches, I think they were used on Delco Light Plants or some other Delco product.