The Hirose DF40TC-10DP-0.4V(58) is a 10-position, 2-row header from the DF40T series, using a 0.016" (0.40mm) pitch. It is a surface-mount plug with outer shroud contacts, designed for board-to-board stacking applications where the mated height above the PCB is 0.045" (1.14mm).
What the 0.40mm Pitch and 1.14mm Stack Height Mean for Your Layout
The board footprint must match this pitch exactly; a 0.50mm or 0.80mm receptacle will not mate. This is the dimension that decides whether the plug fits inside your enclosure's clearance between stacked PCBs.
The DF40TC-10DP-0.4V(58) shares the same 0.016" (0.40mm) pitch, 2-row layout, 0.045" (1.14mm) stack height, and gold contact finish with the DF40TC-20DP-0.4V(58) and DF40TC-30DP-0.4V(58). The decision is purely a circuit-count match — pick the one that equals the number of signals in your harness. All three are active and RoHS compliant.