The 1-647415-1: There is no listed direct replacement from TE Connectivity. For a legacy BOM line, the buying decision hinges on whether the remaining build quantity justifies a last-time buy or a board redesign to a current-series alternative.
The locking ramp fastening provides a positive audible latch when mated with the matching SL-156 header, making it suitable for applications where vibration resistance matters. A polarizing key prevents incorrect orientation during mating.
The SL-156 series is a legacy wire-to-board interconnect family used in power supplies, industrial controls, and appliance harnesses. The 0.156" pitch gives enough spacing for 18-22 AWG wire with good creepage for 250 V applications. The polarizing key means you won't jam the wrong header into it on a rewire.
You need the matching SL-156 crimp terminal (TE part number 640550 series) and a hand crimp tool.