Where the shape comes from
A carpenter’s tool — most often read as a set square or a plumb line, the instrument by which a workman keeps his angles true. The tool stood for the trade, then for the work itself and the person who does it: 工作, 工人, 工厂. As a component it holds up 左 and 巧, and it lends its sound to 功, 红 and 江.
汉字 filed under 工
No published character on HSK Guide is filed under this radical yet. 汉字库.