Where the shape comes from
The hand 又 with a short mark added below the wrist, at the point one cùn down the forearm where the pulse is taken. From that fixed spot it became a unit of length, and in compounds it is a hand doing something measured and deliberate: 对, 封, 射, 寺, and the right-hand half of the simplified 时.
汉字 filed under 寸
No published character on HSK Guide is filed under this radical yet. 汉字库.