The Hirose BM23FR0.6-12DS-0.35V(51) is a 12-position receptacle with center strip contacts from the BM23 series, designed for board-to-board mezzanine stacking at a 0.6mm mated height.
Board Layout: Pitch and Stack Height Drive the Footprint
At 0.35mm pitch, the pad geometry and routing channel width are the tightest constraint on the PCB layout. The 0.024" (0.61mm) height above board and 0.6mm mated stacking height set the z-budget for the mezzanine gap — low enough for clamshell phone designs or stacked PCBs in a handheld enclosure.
The BM23FR0.6-12DS-0.35V(895) shares the same 12 positions, 0.35mm pitch, 0.6mm stack height, gold plating, and solder retention features. For a pick-and-place line running reel-fed parts, either works; for a manual prototype build, the Cut Tape option on the (51) may be more convenient. No footprint or mechanical difference — they drop into the same board layout.