The Universal Service Ordering Code (USOC) system was introduced by AT& T in the 1970's as a means of identifying telecommunication services and equipment. Some of these codes were later adopted by the FCC and are now (usually incorrectly) used universally to describe telephone jacks such as RJ11 and RJ45. Our RJ code table provides the description for RJ codes and provides typical examples for each code.
| Abbreviation | ||
| RJ | Registered Jack | (Prefix) |
| C | Flush or Surface Mount Jack | (Suffix) |
| W | Wall Phone Jack | (Suffix) |
| X | Complex Multi-line or Series type Jack | (Suffix) |
| R J Number | Specific Installation Application |
| RJ11C and RJ11W | Single line phones, accessories, answering machines, and modems |
| RJ14C and RJ14W | Two line phones, accessories and answering machines |
| RJ21X | 1 - 25 single or multiple line circuits bridged to network or customer equip |
| RJ22 | Used for Handsets or Headsets |
| RJ25C | Three-line-phones and accessories |
| RJ31X and RJ38X | Burglar and fire alarms circuits |
| RJ41S and RJ45S | Single line fixed loss loop data installations |
| RJ48C/J and RJ45S | Four wire data circuits |
| RJ61X | Four line phones and accessories |