MTRJ stands for Mechanical Transfer Registered Jack. MTRJ connector is a fiber-optic Cable Connector that is very popular for small form factor devices due to its small size. Housing two fibers and mating together with locating pins on the plug, the MT-RJ comes from the MT connector, which can contain up to 12 fibers.The MT-RJ is one of the newly emerging small form factor connectors that are becoming more common in the networking industry.  Its size is slightly smaller than a standard phone jack and just as easy to connect and disconnect. It's half the size of the SC Connector it was designed to replace.. Compared to single-fiber terminations such as SC, the MT-RJ Connector offers lower Termination cost and greater density for both electronics and cable management hardware. The MT-RJ Connector is significantly lower in cost and smaller in size than the SC Duplex interface.