Sonoff's IP66 waterproof case is compatible with Sonoff Basic, RF R2, TH10, TH16, POW R2 and Dual R2 smart switch relays. Recommended for outdoor or water-exposed use (near aquarium, sink etc.). Compatible with wires between 3 and 6,5 mm diamater.
Basic and RF relays fit entirely, and other bigger Sonoff relays (TH10, TH16, Dual) without cover.