The form of crochet known as Tunisian crochet takes a certain kind of crochet hook , or Afghan crochet, is worked in a slightly different way than basic crochet. A number of stitches are collected on the hook before being worked on the next row. This requires a longer hook and one that has a stopper at the end so that the stitches won’t fall off.
Some of the newer hooks have a flexible cord, rather than being long and straight. These hooks are known as Tunisian or, sometimes tricot hooks. They usually come in only medium to large sizes, but it is not impossible that some finer Tunisian hooks exist as there are examples of purses worked in this form of crochet using fine threads.
There are also double-ended hooks with a different size at each end. These are just a means of cutting down on the number of hooks you need, which is especially useful when traveling. But double-ended hooks with the same size at each end are a different matter these are for working a form of Tunisian crochet in two colors.