Siemens IE FC M12 Plug PRO 4x2 Compact Operating Instructions page 16

Installation
6. Shorten the inserted wires flush with the edge of the loader housing.
7. Screw the loader and the connector housing together. When joining the two parts,
make sure that the guide notch on the loader engages the spring of the connector
housing. The two parts must be securely screwed together so that the insulation
piercing terminals can cut through the wire insulation ensuring reliable contact
between the wire and the terminal.
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IE FC M12 Plug PRO 4x2
A5E03679115A-AC,05/2015