纲

The silk-thread radical on the left places 纲 in the thread-and-cord family — 线 thread, 绳 rope, 网 net. Originally 纲 named the main cord of a fishing net, the thick rope that holds everything together. From there it generalised to "guiding principle" — the rope that organises the whole.

冈 supplies the sound gāng unchanged. Its picture — a mountain ridge — adds a faint semantic echo: a ridge is a long firm line running across terrain, much like the main cord running through a net. Same phonetic in 钢 steel, 刚 just-now (firm), 岗 sentry post.