RJ11/RJ12 Splitter/adapter terminoligy


I am currently looking for the correct terminology for purchasing RJ Splitters. It appears you can purchase both a straight through splitter in which all 3 female ports are connected in parallel (pin 1,2,3,4… on Female port 1 is connected to pin 1,2,3,4… on female port 2 & 3). You can also purchase a phone line splitter that is used for a phone line that has 2 separate lines. Line 1 is on pin 1/2 and line 2 is on pin 3/4. In the line splitter the wires from female port 1 to female port 2 are not the same connection points as female port 1 to female port 3 (pin 1&2 on Female port 1 go to pin 1&2 on port 2. Pin 3&4 on Female port 1 go to pin 1&2 on female port 3).

Actual pin numbers may vary based on the connector, but what I am searching for is a way to ensure I am getting a straight parallel connection for my splitter, and not a cross over type connection.

Terminology seems to be inconstant throughout the internet and through different retailers.


Hello @electrical_peter,

In general most parts that would be a splitter are just that splitting the signal and you would not see a change. In an adapter you will have adapters. @Lindsay_1029 had a post on Straight vs Reverse modular cables. This should be called out in the datasheet. -Robert


Hi Robert,

Thank you for your quick reply to this subject. I feel I have a decent grasp on Modular cables and how they identify, but when searching for a straight through ‘T’ splitter to continue all lines of data from a RJ12 or RJ11 cable, the “straight through” portion is not always called out. Datasheets would be ideal, but they are not available in all cases. I was hoping there was a standard naming convention.

When you say “in adapters you will have adapters” do you mean that if the female to dual female connector is called an adapter, that it will not act as a splitter (splitting the signal, but not changing the pinouts), but it will actually do something to change how the lines connect to each other?

Below is an example of a supplier using both adapter and splitter to define this component.


Hello Peter,

Without a data sheet it is hard to identify the specifications on a product. Even harder is to find dealers who will not even provide a data sheet to use commonly acceptable terms.

At first glance on this part they use the word reversed pinout so I would say this is not a straight splitter. When in doubt ask for the data sheet. If not available I would look for a different dealer as this information should be available to you.