A crochet hook (or crochet needle) is an implement used to make loops in thread or yarn and to interlock them into crochet stitches. It is basically a round shaft pointed on one end, with a lateral groove behind it.
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The two basic ways of holding a crochet hook are:
the pencil grip, with the hook going over the crotch of the thumb, resembling a pencil,
the knife grip, with the hook under the palm of the hand, resembling a knife held when held overhand.
These grips are functionally equivalent and selected as a matter of personal preference, with hybrid forms being commonplace.