FC stands for Fixed Connection. It is fixed by way of threaded barrel housing. FC connectors are typical in test environments and for single mode applications. FC connectors were designed for use in high-vibration environments. The FC Connector is the most popular connector used today. It can be seen in every area of the communications environment, from a telecom´s distribution room to a LAN closet, the FC has set the standard for optical Fiber connectors. FCS are being replaced by SC and LC connectors.

ST stands for Straight Tip - a quick release bayonet style Connector developed by AT&T. STs were predominant in the late 80s and early 90s.

Features:

Low insertion loss(≤ 0.20dB)and high return loss(≥ 55 dB)
Free-floating ceramic ferrule
UL-rated plastic housing and boot
Boots in a variety of colors
High precision alignment connector

Applications:

Local Area Networks (LANs) and Wide Area Networks (WANs)
Fiber Optic CATV, FTTH, FTTB, FTTP etc
Fiber Optic telecommunication systems
Transmission Mode (ATM)
Fiber Optic Backbone
Military Instrumentation