The 'stopping' radical, named after the Yijing trigram for mountain (☶) which signifies stillness and a halt. Indexes a tiny set: 良 (good), 艰 (difficult). Low productivity, but visually distinctive enough that almost any character containing the 艮 block (恨, 限, 跟, 很, 银) feels related at a glance — though most of those file under their other radicals.