Depending on the yarn size I would say a C hook or a size 7 steel hook for fingering yarn. The steel hook is great for weaving and is very useful to use when fixing knitted stitches. If the yarn is very fine then you might want a smaller hook which would be 9 or up a size. With steel hooks the larger the number the smaller or finer the head of the hook. So with really lacy yarn you might even want a size 10 or 11.