"For nominal sizes below 0.5mm, the deviations shall be indicated adjacent to the relevent nominal size(s)"
I would ask the supplier of the drawing what they want applying to the dimension. It's likely they (like me) didnt realise the standard stopped at 0.5mm. Be prepared to suggest a tolerance yourself as it may be possible they have no idea what would be considered reasonable in that range.
Will Walters
Sheffield UK
Designer of machine tools - user of modified screws