The 640251-4 is a 4-position single-row receptacle housing on 0.156" (3.96mm) pitch — the same pitch as the SL-156 series pin headers. That means the board layout for the mating header is set at 3.96mm centre-to-centre, and the housing will align only with a matching 4-position header of the same pitch.
Sourcing the crimp terminals separately
Without the terminals, the housing is just a shell; the harness won't conduct. Termination is crimp, so the wire gauge and tooling for the SL-156 terminal determine the current capacity. The housing itself does not add a current limit beyond what the terminal and wire can handle.
Free-hanging inline mounting and mating
The connector type is receptacle, accepting a female socket contact.