The Hirose DF30FC-40DS-0.4V(82) is a 40-position receptacle from the DF30 series, designed for board-to-board parallel stacking. Gold plating on the contacts (2.00µin) is a light flash — adequate for a few mating cycles in a permanent assembly, but not a high-cycle field-service connector.
Mated Stacking Height — The Dimension That Decides Fit
The mated stacking height is 0.9mm. This is the single dimension that determines whether this receptacle mates with the intended header — if your board-to-board gap is anything other than 0.9mm, this part will not fit. The 0.40mm pitch means the PCB footprint is tight; routing traces between pads requires a capable board house.