From the 1920's up to the 1960's the Bell System and Western Electric used vast oceans of black phenolic plastic for tube sockets, telephones and thousands of other communications products. If you want that look for your audio project here's an affordable bargain socket for you. Can be top chassis or bottom chassis mounted. For top chassis mounting the bore hole must be larger than 1.149". For bottom chassis mounting the bore hole must be larger than 1.334". Screw mounting centers 1.505". Brand New.