The D4 connector is probably the first connector to use ceramic or hybrid ceramic/stainless steel ferrules.
It uses a smaller ferrule than SCs or FCs. It was widely used in telco networks in the 80s to early 90s and some may still be in use.
Location key structure have high precision alignment
Corrosion resistant body (Nickel plated brass)
Spring style ferrule
Variety of boot colors
Low insertion loss and back reflection loss
Comply with ROHS
Fiber optic communication system and telecommunication networks
Fiber optic data transmission
Optical access network
Fibre to the Subscriber (FTTx) applications
Optical cable interconnection