The TE Connectivity 173851-1 is a 12-circuit, 2-row plug housing from the Multi-Lock series, designed for free-hanging inline wire-to-wire or wire-to-board harness applications. It uses a 3.50 mm pitch and a 5.90 mm row spacing, with a latch holder for positive retention against vibration. This is a crimp-and-poke housing — the contacts are ordered separately.
The 3.50 mm pitch and 2-row layout are shared across the Multi-Lock series, so the mating receptacle must match both the pitch and the row count.
No official cross-reference or second-source is on record; the 1-1644055-3 is a 6-circuit plug in the same series but with a 6.35 mm pitch and different row spacing, so it is not a functional substitute for this 12-circuit, 3.50 mm pitch housing.