When central banks raise or lower interest rates the radio announcer will say for example:
an increase of one half of one percent
Informally people use half a percent instead, which is less wordy, but is it also incorrect? Ngrams analysis shows publishers favour the longer version, although the short form seems to be gaining some traction.
Thinking about it, I'd never offer someone one half of one pizza; that sounds weird. However, I believe of is necessary here, in combination with an article, quantifier or pronoun. Is this correct?