RJ21

RJ-21 (or RJ21) is a registered jack standard for a modular connector using 50 conductors, usually used to implement a 25-line (or less) telephone connection. It's also known as a 50-pin telco connector, or an Amphenol connector. (The latter is a genericized trademark, as Amphenol was the largest manufacturer of these at one time.)

Dual RJ-21 connectors are often used on punch blocks to make a breakout box for PBX and other key telephone systems.

The same connector is used for SCSI-1 connections. Computer printers use a shorter 36-pin version known as a Centronics connector.

v • d • e USOC registered jacks
RJ9 • RJ11 • RJ12 • RJ14 • RJ21 • RJ25 • RJ45 • RJ48 • RJ50 • RJ61

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