Besides the original use for bridged connections of telephone lines, the RJ12 / 6P6C is often used for:

• Guide ports on mounts
• Connection between hand controller and the HC port on the mount
• connection between different electronics on a mount like the iEQ45 Pro

Example picture: left is a RJ12 6P6C and on the right a RJ9  4P4C plug

see also: Modular connector - Wikipedia

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