What this Zener TVS does in the assembly
With a reverse standoff voltage of 11.4V and a clamping voltage of 21V at 23.8A peak pulse current, it protects 12V nominal rails from surges up to that energy level.
Sizing for the rail and the environment
It is a through-hole axial package (B, Axial), so it swaps into a board with plated through-holes — no reflow, no hot-air station. A field-service kit with a soldering iron and a desoldering pump is enough to replace it on site.
The part is, so it arrives loose in a bag or tube — fine for hand-assembly or low-volume builds, but not reel-fed for automated pick-and-place.