The fiber end is embedded in a 2.5 mm ferrule made of ceramic or. 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, 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.
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