Which of the following connector types is only used for Coaxial?

RJ-11 is a 6-position modular connector used for telephone lines and DSL connections, designed for twisted-pair copper wire, not coaxial cable.

ST (Straight Tip) is a bayonet-style fiber optic connector used for multimode fiber networks, and is not associated with coaxial cable at all.

The F connector is a threaded coaxial RF connector used for cable television (CATV), satellite dish, and cable modem connections. Its design uses the center conductor of the coaxial cable itself as the pin, and the threaded barrel engages the coaxial cable's outer shield - making it inherently and exclusively a coaxial connector type.

RJ-45 is an 8-position modular connector used for Ethernet networking over twisted-pair copper cable (Cat5e, Cat6, etc.) and has no application with coaxial cable.