For nut M 2 (flat) + nut M 3. For real pleasure in modelling a comprehensive set of tools is indispensable, as it ensure that you always have the right tool for the job on hand.
These small open-ended spanners are perfect for tightening or undoing standard and self-locking nuts, in the sizes M 2, M 2.5, M 3, M 4 etc.
The range available covers all the sizes which are required for a model helicopter.