Here's a really handy accessory for tube amp builders. Use these and you won't have to drill a bunch of ventilation holes in your chassis. Nickel plated steel plate measures 2.522" X 2.522". Socket hole 1.072"/27.23mm, tube socket screw mounting centers 1.485"/37.72mm. Bottom mount octal tube socket 81003 on the Angela Instruments website fits this plate exactly. Please note that these plates are fabricated on automatic machinery with not a lot of attention lavished on an elegant finish. There are typically some small scratches and marks in the steel under the nickel plated finish.The bottom line? These plates look good enough for most D.I.Y. tube amp projects but if you're really fussy you may want to make your own plates. The finish on these plates could be better. I'd powder coat these or use a hard catalyzed epoxy type paint like Sherwin Williams Polane.