An electronic device may have metal structures such as metal electronic device housing structures and other conductive structures. The conductive structures may have a slot or other opening. An antenna may be formed from the conductive structures. Control circuitry in the electronic device may receive input from input-output devices and may use the input-output devices to provide a user with output. The control circuitry may be coupled to a radio-frequency transceiver that is used to transmit and receive wireless communications. The radio-frequency transceiver may be coupled to the antenna using a transmission line. The transmission line may have a radio-frequency connector that is coupled to a radio-frequency connector on an antenna feed bolt. The antenna feed bolt may have a shaft that spans the opening in the conductive structures and may be coupled to antenna feed terminals on opposing sides of the opening. The antenna may have a tuning bolt.