This is the Super resistant K design, meaning the housing and internals are built for higher ambient temperatures and aggressive atmospheres — halogen-free and silicon-free, so it won't outgas or corrode sensitive contacts in sealed enclosures.
The 16 A rating holds at 30 °C ambient, but drops to 15.2 A at 40 °C, 14.4 A at 50 °C, and 12.32 A at 70 °C. That 20 kA figure is the one to use for industrial panel SCCR calculations — it tells you the device can safely interrupt a 20 kA prospective fault current at 230/400 V without welding or exploding.
Physical fit and mounting
Width is 36 mm (2 modular units), depth 77 mm, height 90 mm, with an installation depth of 70 mm behind the panel face. The IP20 rating applies when installed in a distribution board with conductors connected; the device itself isn't rated for wet or dusty environments, so keep it inside the enclosure.