another RT insulator found at the dump site. Following info quoted from Jack Tod's book Porcelain Insulators (1988) page 134 "The S T variation indicated insulators of the "Silent Type"their trade name for radio-free insulators. The small indenture under either marking after the mid- 1960's signifies the insulator neck is compatible with preformed tie wires". Modern technology at it's finest. Who would have ever thunk it.