RJ100 - Cat10

A palindromic twisted pair cable connector.

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"You know those guitars that are like, double guitars?"
- Otto Warmbier

The time-tested RJ45 connector has served societies around the world remarkably well! It is cheap, fairly rugged & can be terminated in seconds. With the advent of HDBaseT, the RJ45 connector is being pushed to the theoretical limit.

Why not double the contact count?

In recent years we've seen the introduction of the "Lightning" connector, soon followed by USB C. Both have a palindromic design -- there's no wrong way to connect it to a receptacle. The RJ connector family could be next!

The concept is simple: contacts on the top of the connector are the mirror image of contacts on the bottom of the connector. It is effectively 2X ethernet cables in 1. This new cable could be referred to as Cat10.

This proposed connector would still be compatible with all existing RJ45 receptacles... and could even have the mere traditional 8 wires found in an ethernet cable terminated to it (e.g. a "half-speed" cable). These "half-speed" ethernet cables would have both sides of the connector terminated to the same set of wires.

The concept does present a few new challenges:

  1. Latching: the delicate latch found on all RJ connectors would be absent. Instead, the proposed design features a pair of voids on each side of the connector. Latching, if necessary, would be provided by the receptacle. The connector doesn't need a latch, though. Friction is often sufficient.
  2. Crimping:
    1. All-new crimp tools would be required.
    2. The contacts in each connector would need to be shorter so no connection is made between the two sets of eight contacts. 
    3. RJ100 receptacles would not support RJ45 connectors. While the two are technically pin-compatible, an RJ100 receptacle would be shorter than an RJ45 connector.
  3. Slightly increased risk of interference.

What do you think? Print a few sample connectors if you'd like...

Next Steps:

  • Creating a fully-functional 2x RJ45 to 1x RJ100 adapter
  • Creating a fully-functional RJ100 connector
  • Creating a fully-functional Cat10 cable


A sample RJ100 connector model.

Standard Tesselated Geometry - 44.44 kB - 06/13/2019 at 02:35



Code used to generate the sample RJ100 connector model.

scad - 1.69 kB - 06/13/2019 at 02:35


  • Preparing for Use

    William01/02/2023 at 04:00 0 comments

    While working on a new pin specification for the Retro Modules project & a new project related to a Starlink PoE Injector (coming soon!), I realized I needed to define a 2.54mm header specification for this project.

    This project isn't re-inventing the wheel -- just adding one.

    The color code for ethernet cables is based on the 25 Pair Color Code. The spec below is as well.


    Contact Pair Role Primary Wire Color Secondary Wire Color
    1 2 DA+ white orange
    2 2 DA− orange white*
    3 3 DB+ white green
    4 1 DC+ blue white*
    5 1 DC− white blue
    6 3 DB− green white*
    7 4 DD+ white brown
    8 4 DD− brown white*
    9 8 DH− green red
    10 8 DH+ red green
    11 7 DF− orange red
    12 5 DG− white slate
    13 5 DG+ slate white
    14 7 DF+ red orange
    15 6 DE− blue red
    16 6 DE+ red blue

    * Optional Secondary Wire Color

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