finger's breadth
Noun
Meaning
the length of breadth of a finger used as a linear measure
Source: WordNetSynonyms
Hypernyms
Examples
One of the sayings of Diogenes was that most men were within a finger's breadth of being mad; for if a man walked with his middle finger pointing out, folks would think him mad, but not so if it were his forefinger.
Most men are within a finger's breadth of being mad.