Knitting is done on two pointed needles of the same size. One needle holds the finished work while the other creates the next row. You finish one row, turn, and work back. Knitting may also be done on double-pointed needles, which are used for knitting in the round and for special stitches, such as cables, or circular needles, which look like two single-pointed needles joined by a plastic strand. Circular needles are used to knit in the round without seams for such things as hats and collars. Knitting needles are sized by number (as well as millimeter).
Crocheting is done with a single hook. Each stitch is worked into a stitch in a previous row and slipped off the hook. You can crochet in rows or go round and round. The thickest part of the hook is the part used to determine the size of the hook. If you are crocheting too tightly, perhaps you are not sliding the work back far enough onto the hook. Crochet hooks are sized by letters of the alphabet.