Handy accessory for tube conversions, repairs, experimentation. Outer diameter 1.693"/1 11/16". Socket hole .881"/7/8". Tube socket screw mounting centers approximately 1.327" but the slots allow for some fooling around. Please note that these plates are stamped out on automatic machinery with not a lot of attention lavished on an elegant finish. There are some small scratches and marks in the brushed finish. Bolts down to the chassis on the screws used to mount an octal socket. I tried installing a number of the fine sockets we sell on this plate and most fit pretty well, especially top chassis mount sockets.