They are engineered systems designed to protect fiber splices from mechanical stress, environmental exposure, and long-term performance degradation. Horizontal fiber optic splice closures, also known as optical cable splice boxes, play an important role in the communications industry. It is used to connect two or more optical cables together and provide complete. An optical cable split fiber box, also known as a fiber distribution box or fiber optic splice closure, is a device used to terminate, splice, and distribute optical fibers. It typically consists of two parts: an outer housing and an internal structure.