What this connector is
The Amphenol FCI 79821-404HLF is a dual-row board-to-board header in the BERGSTIK II series — 4 positions on 0.100" (2.54 mm) pitch in a 2-row layout, with both rows spaced 0.100" apart, giving a 4-circuit footprint for stacking or coupling daughter cards to a backplane or mother board. The push-pull fastening type relies on contact friction and header-to-socket housing retention rather than a screw-lock or latch tab. Contacts are square male pins in phosphor bronze with tin plating on both the mating face and the solder-tail side (100 µin thickness on the mating surface), and the insulator is UL94 V-0 rated black liquid crystal polymer. Rated 5 A per contact at the circuit level and 110 V on the dielectric.
What the ratings mean for fit
Pitch is the 0.100" (2.54 mm) board-to-board standard — the same foot print as a standard 0.100" strip header, so it drops into a standard dual-row footprint without routing changes if the circuit count matches. The 4-position count is small; a board with a 4-circuit signal or low-power bus line is the natural fit. The 5 A per-contact rating handles moderate power or mixed-signal duty at board-to-board stack voltage; 110 V is the dielectric ceiling — adequate for logic-level or low-voltage power distribution within a closed chassis. The post length is 0.200" (5.08 mm) on the solder side, so the board needs a 0.200"+ pad depth; the insulation height of 0.100" (2.54 mm) sets the mated stack gap. Tin-on-tin on both sides is the finish story: it gives good solderability and decent first-mate resistance but limits re-mating cycles compared to gold. For a permanent board-stack installation the tin finish is perfectly adequate. The unshrouded header has no keying protection — alignment and polarity management depend entirely on the mating receptacle housing and the board keep-out around the header.
Sourcing posture
Listed Active. 4 positions, dual-row BERGSTIK II — quoted to order against the BOM quantity. Confirm the exact position count and the mating half before committing. No official successor order code.