Does anyone know what the letters "T", "S", and "TS" stand for at the end of many older spark plug numbers?

For example, when AC changed it's numbering scheme, AC plug 86 became the AC recommended plug for the 29 Plymouth, but there is also an "86S" Plug.  Blue Crown also had an "86" and an "86S" plug.  The Edison plug was "43", "43T", or "43TS"