It carries a 16 A rated current with C characteristic for short-circuit and overload protection, plus a Type A residual current device rated at 300 mA. The C characteristic (10× to 20× In magnetic trip) suits motor and lighting circuits where inrush is higher than a B-curve would tolerate without nuisance tripping.
In a crowded consumer unit or sub-distribution board, that 2-module footprint matters — it leaves room for surge arrestors or additional RCBOs in the same row. The busbar comb bridges across the line terminals; no special wiring adapter needed.