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 .868"/22.05mm, tube socket screw mounting centers 1.119"/28.44mm. Top mount 9 pin tube socket 949601 fits this plate exactly. We've also got a bottom mount white ceramic tube socket 992413 fits. 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.