RJ-11 Dimensions
The RJ 11 connector sizes differ, but most of them are between 2 to 4 inches long. Majority are square-like in shape, but this isn’t always the case.
What is RJ 11?
RJ 11 is the usual connector applied for 2 pair, 4 wire phone wires. The initials RJ connote registered jack. The registered jack refers to a connector utilized with phone wire terminals. The RJ 11 connector has half a dozen connector positions. For the most part though, only a couple are actually utilized. At most, four are used.
There are two kinds of connector wirings for this registered jack: the UTP (Unshielded Twisted Pair) and flat-satin cable (untwined).
Widespread Use
The reason why there are many RJ 11 connector sizes is because of its widespread use. Practically all POTS phone jacks in US offices and homes use RJ 11. Many single line phone jacks also use RJ 11 as the connector.
Other Registered Jacks
It should be stressed that there are many other kinds of RJs. RJ 61 is for a four-line phone jack. RJ 24 is made for a three-line phone jack. The RJ 14 connector is designed for a two-line phone jack. All these registered jacks make use of six-position modular connectors.
Application of RJ 11 Connectors 
As stated, the RJ 11 jack makes use of two of the six positions. This allows it to be linked to the 6P2C modular jack. But it should be stated that these connectors are hardly utilized. Most frequently, the jack is used as a 6P4C jack. A couple of the wires are not used on the junction box.
The additional wires however, can be employed in various applications. Some of its uses include stopping the ring of a pulse dial phone. The extra wires can be used as LED indicators. It can also be applied for certain ringers.
Pins
Pins 2 and 5 are used for transmitting DC or AC power. This is carried from a jack close by or a plugged in transformer. This provides power to the jacks.
Majority of the time, the phone line allocates the power to the terminals. In old telephone terminals, incandescent lights were included. Compared with the modern terminals, they require more energy.
If you are having a telephone installed, chances are it will use the RJ 11 connector sizes mentioned here. But you could also end up using the other jacks indicated. Check with an expert if you are not sure.
