The 644753-6: Six positions in a single row is a common count for power and signal in a wire-to-board interconnect. The header is fully loaded — all six positions are active, no empty slots.
Current rating — it follows the wire, not the pin
For a given load, size the wire to the ampacity; the connector won't be the bottleneck. The 600VAC voltage rating covers line-voltage equipment in control panels and machinery.
This header mates with standard MTA-156 receptacle housings and their crimp sockets. The 0.156" pitch is a TE Connectivity standard — it does not directly cross to Molex 3.96mm connectors, which use a different keying and latch geometry.