Here's a really handy accessory for tube amp builders. Mount this plate on the top of your metal chassis and you won't have to drill a bunch of ventilation holes in your chassis. Black steel plate measures 2.647" X 2.647". Socket hole 1.060", tube socket screw mounting centers 1.440". Bottom mount octal tube socket 81003 on the Angela Instruments web site fits this plate exactly and is included installed. We also included rubber shock mounting grommets.