DF40C-20DP-0.4V(51) from Hirose Electric Co Ltd is a compact rectangular board-to-board connector plug designed for high-density interconnect applications where space, stacking flexibility, and assembly reliability matter. With a fine 0.40 mm pitch, 20 positions, dual-row layout, SMT mounting, and solder retention feature, it is well suited for portable electronics, industrial control modules, compact embedded systems, display assemblies, and communication devices. The listed mated stacking height options support designers who need low-profile interconnects across tightly constrained PCB layouts. As an active Hirose connector with sufficient supply status, it fits both ongoing production and maintenance sourcing needs, although engineers should still review long-term availability for program planning. RoHS compliance information is not explicitly provided in the input data, so official manufacturer documentation should be checked before use in regulated markets. For procurement-sensitive designs, attention should also be paid to storage handling, packaging format, and open-market counterfeit exposure.