Quick answer
Internationally trained nurses need Grade B (350) in each of the four OET sub-tests for NMC (UK), NMBI (Ireland), and AHPRA (Australia) registration. Uniquely, the NMC accepts Grade C+ (300) in Writing if the other three sub-tests reach Grade B in the same or combined sittings within 6 months. Writing is the most retaken sub-test — typically because of Conciseness & Clarity losses from over-including case notes.