Tube socket mounting hole measures 28.50mm. Plate measures approximately 53.89mm X 45.06mm. Tube socket screw mounting holes are 35.60mm apart. Centers of the two long slotted plate mounting holes are 42.23mm apart; this feature allows you some latitude in your mounting requirements. Handy for mounting 4, 5, 6, 7 and 8 pin tube sockets to your chassis.