The 2-178128-4: It uses a 0.200" (5.08mm) pitch, giving each circuit enough spacing for moderate power or signal in a wire-to-board harness. A polarizing key on the housing prevents mismating with the header — useful when multiple Dynamic connectors sit side-by-side in the same assembly. This is a crimp-termination, free-hanging (in-line) receptacle. The Dynamic D-3200 series is a modular power and signal interconnect family; this single-row 4-position variant is a compact choice for a low-circuit-count harness branch.
The 2-178128-4 requires separately ordered female socket contacts. TE's Dynamic D-3200 series uses a specific crimp terminal — look for the mating socket contact in the same series (typically the 1-178128-* or 178128-* family). The housing is keyed and single-row, so the terminal insertion orientation matters: the contact must seat fully until the retention lance locks into the housing cavity. A terminal position assurance (TPA) retainer is not standard on this single-row housing, so verify full insertion by feel and a gentle pull-back on the wire.