DF40HC(4.0)-50DS-0.4V(51) from Hirose Electric Co Ltd is a fine-pitch rectangular board-to-board receptacle designed for compact, high-density electronic assemblies. With 50 positions, 0.40 mm pitch, dual-row construction, and a 4 mm mated stacking height, it fits space-constrained designs that need reliable interconnect performance in portable, industrial, communications, and embedded systems. Engineers typically select this series when low-profile SMT mounting, precise board stacking, and established Hirose connector quality are important to long-term product design. The listed product status is Active, which is a positive indicator for ongoing design support, although the supplied lifecycle field remains unknown and should still be verified through current manufacturer documentation for new programs. RoHS compliance information is not explicitly provided in the supplied specifications, so a formal compliance conclusion cannot be confirmed here. For regulated applications, buyers should request the latest RoHS and related material declarations directly from the manufacturer or authorized source before release to production.