The table below summarises the plug types, voltage and frequency of electrical current in both Belgium and Nauru.
|Frequency of electrical current||50Hz||50Hz|
Belgium uses Plug Type E.
You will need this adaptor:
Socket Type E
(Belgium) to Plug Type I
The voltages found in Belgium (230V) and Nauru (240V) are not exactly the same, but the difference is tolerable, so you should not need a transformer.
The frequency found in Belgium and Nauru is exactly the same (50Hz). Timing devices and appliances that use motors will function as expected under this frequency.