The Amphenol FCI BERGSTIK II 87185-126HLF is a 26-position single-row unshrouded board-to-board header on the standard 0.100" (2.54 mm) pitch.
The 26 positions on a single row is a less common count than 24 or 30, so verify your BOM line exactly before committing. The 0.095" (2.41 mm) post length below the insulator tells you the board thickness and solder fillet clearance it's designed for — standard 1.6 mm PCB with room for a good through-hole solder joint.
Within the BERGSTIK II family, the 26-position 87185-126HLF sits between the 24-position and 30-position variants at the same 0.100" pitch. The decision is purely position count: if your board has a 26-position footprint, this is the one. The 30 µ" gold plating is the standard durability option for this series — the GXT finish is Amphenol FCI's own enhanced gold alloy, but the thickness spec is the same. No other functional difference in current rating, voltage, or mating style across the position variants.