(さいぶ) A detail of a 3-dimensional thing:a machine part or body part.
(しょうさい) The details – used when explaining. This is the one Windows uses when it gives you an error message:To see the details of the problem, click here.   TTT
かい(こまかい) Details of a flat, 2-dimensional pattern. Also this is the expression you use when you say, ‘Don’t sweat the details.’