Weld Draglite

Might someone have a 15 X10 with 5.5 backspacing or a 15 X 12 with 6.5 backspacing Draglite that take a measurement?
I am looking for the dimension on the out side (yes, the shiny side) at the narrowest point across inside the barrel

I have Draglites that are 15x12 with a 5 1/2 back spacing, measuring across I came up with a 12 3/8 per your drawing at the end of the studs. Doug

Thanks