This unusual version of the classic FT92 insulator, made of an unknown (to me) material, was produced for STIPEL, TELVE and TIMO telephone companies (*) in the 50s. Here you see a rubber ribbon has been used to protect the insulator groove and separate it from the copper wire

(*) STIPEL... Società Telefonica Interregionale Piemonte E Lombardia TEL.VE. .. TELefonica Veneta TIMO ....... Telefonica Interregionale Medio Orientale

These companies, with SET and TETI gave life, in the 60s, to th, Italian State Telephone Company called SIP