The 350434-1 is a 15-position, 3-row vertical header from TE's Universal MATE-N-LOK series, designed as the board-mounted half for a board-to-cable/wire connection. The 0.250" (6.35 mm) pitch and row spacing create a uniform square grid on the PCB — every hole is 6.35 mm from its neighbour, which simplifies the footprint layout but does consume more board area than a staggered pattern. The locking ramp fastening means the mating connector clicks into place and stays there under vibration — no jack screws or secondary hardware needed.
The insulation material is polyamide (nylon) with a UL94 V-2 flammability rating. V-2 allows some burning with flaming drips — acceptable for most general-purpose equipment inside an enclosure, but if the application requires no flaming drips (e.g., certain appliance or lighting standards), a V-0 rated housing would be specified instead.