FC connector
The fiber end is embedded in a 2.5 mm ferrule made of zirconia ceramic or stainless steel. The tip is then typically polished to produce a rounded surface, called "physical contact" polish. This surface profile means that when the fibers are mated they touch only at their cores, allowing transmission with low loss. The fibers are spring-loaded to control the force as the plug is screwed into the receptacle. A key prevents the fiber from rotating while the connectors are being mated.