Sennheiser CI1 is a spare cable, locking Sennheiser minijack to 1/8″ right angle stereo minijack.
This cable is used to output signal from your camera-mount receiver (EK100 or EK500) to the mini-jack input on video camera.
It works for the current G4 series, along with older G3 and G2 series camera mount (ENG style) receivers.
CL1 is a genuine Sennheiser accessory / spare.
The locking ring matches perfectly with your camera-mount receiver output, while the right-angle 3.5mm is TRS wired for dual mono, and is perfect for a low-profile application, avoiding strain on your device input socket.