Hey....I'm also curious about the t-slot receptacle as well as the 4 prong holed receptacles....I'd guess the 4 prongs were the fore runners to the t slots?
If you look it looks like on the 4 prongs the two tandem blades are very similar to the standard 6-15 receptacle minus the ground prong...or the horizontal slots on the t-slot receptacle.
I'd like to know what the tandem blade plugs were used on? It looks like it was obviously a 240 volt power source with a 10-15 amp max draw load.
Anyone know?
