The TE Connectivity 4-5177986-5 is a 120-position plug from the Free Height (FH) series, designed for mezzanine board-to-board stacking. It uses a 0.031" (0.80mm) pitch in two rows, with center strip contacts — the signal path runs through the middle of the connector body, which keeps routing channels clear underneath on the PCB. The plug stands 0.309" (7.85mm) above the board, and mates with the matching FH receptacle to achieve stacking heights of 8mm, 12mm, 16mm, or 20mm. That range from a single plug is the main selection variable: you pick the receptacle height to hit the board spacing your enclosure needs.
What the 8 µ" gold plating means for the duty
That thickness suits a board-to-board interconnect that mates during final assembly and stays mated.
Board guide and SMT mounting
The plug includes an integral board guide — a molded alignment feature that engages the receptacle before the fine-pitch contacts touch. On a 120-position, 0.80mm pitch connector, that guide is what prevents bent contacts when two PCBs are brought together slightly off-angle. It's a surface-mount part, so it goes through reflow with the rest of the board. The Tape & Reel packaging (Cut Tape option available) feeds into a standard pick-and-place line.