The Hirose DF12B(5.0)-40DP-0.5V(86) is a 40-position, dual-row board-to-board header from the DF12 series, built for mezzanine stacking at a 5mm mated height.
What Crosses Into the Harness I've Got
If you're replacing this on an existing assembly, the 5mm mated stack height is the dimension that matters — it sets the board-to-board spacing. The 0.50mm pitch and 40 positions are fixed; the mating receptacle must match both. The DF12 series uses the same 0.50mm pitch across its range, so a 40-position receptacle from the same family with a 5mm stack height is what you'd look for. The gold plating (8.00µin) is standard for this series — it's fine for typical signal-level mating cycles, but if the original application saw heavy reconnection, the plating thickness is worth matching.