The Amphenol 87900-156HLF is a BERGSTIK® II series unshrouded male pin header, 56 positions loaded in a dual-row arrangement on 0.100" (2.54mm) pitch. It's a through-hole solder-terminated board-to-board interconnect — the long 0.720" mating contact length gives good wipe for repeated board stacking or cable-to-board applications.
The 0.100" pitch and 0.100" row spacing match the standard 0.100 x 0.100 grid — a common footprint for legacy backplanes and prototyping boards. The 0.120" solder post length is short; it's meant for standard 0.062" PCBs, not thick backplanes.