Where the shape comes from
Read one way as a variant of 足, a leg or foot, and read another as a folded bolt of cloth ready for market, the two accounts never quite reconciled even in the old dictionaries. It survives today mainly as the measure word for a bolt of cloth or a horse, and as a rare dictionary classifier for a small set of characters, among them 疏, to unclog, to be sparse, whose own history is tangled enough that scholars still debate how much of it this radical actually explains.
汉字 filed under 疋
No published character on HSK Guide is filed under this radical yet. 汉字库.