The ST connector’s keyed bayonet design is similar to that of a BNC (Bayonet Nut Connector or Bayonet Neill-Concelman) connector. The connector is used widely for MMF and SMF FOC and is extremely easy to use. The ST connector is manufactured in two versions – the ST and the ST-II. Both types are keyed and spring loaded, and use a “push-in and twist” mechanism..