The 3-643817-4: It uses an IDC (Insulation Displacement Connection) slot that pierces 18 AWG wire insulation as you press the cap down, making it a fast field-repairable option for harness builders. The orange housing colour is a visual cue for the 18 AWG wire gauge variant in the MTA-156 line, so you can grab the right connector from a bin without reading the part number. The closed-end design and polarizing key prevent mis-mating with the wrong header orientation.
This receptacle accepts 18 AWG discrete or ribbon cable through its IDC slot. No crimp tool needed — you lay the unstripped wire across the slot and press the cap down with a simple hand press or arbor press. The tin-plated contacts (80.0µin / 2.03µm thickness) provide adequate corrosion resistance for indoor equipment applications; for high-cycle or corrosive environments, the gold-plated variants in the MTA-156 family are the better call. It mates with the matching MTA-156 pin header (straight or right-angle, through-hole or surface-mount) at the same 0.156" pitch.