Hook tools and their easier-to-manufacture modern equivalents, ring tools, are left over from the time when lathes were human powered. The easiest way to visualize a hook tool is to think of bending the leading inch of a roughing-out gouge up at a right angle (see the illustration below). This configuration allows you to present the edge of the tool at the bottom of a bowl. The tool is most prevalent in Scandinavia, where its use has never entirely died out.
If properly sharpened, hook tools are efficient, but they are designed for very low speeds such as those you would encounter in spring-pole lathes. I cannot emphasize enough that speeds of 1 50 rpm to 250 rpm are a must when using this tool for faceplate work. Hooks are dangerous at high turning speeds.
To use the tool, place it level (or even pointed slightly downhill) on the rest. Roll it left about 45° so that the face of the cutting edge is pointed to about 10 o’clock, and swing it in an arc to create bowls. In Scandinavia, turners put a fulcrum pin in the middle of their tool rests to lever the shank of the hook. This makes the tool both more efficient and easier to swing in a pleasing arc. For faceplate work on a modern lathe, I do not find hooks as efficient as a good HSS bowl gouge.
Hooks work in hollow spindle work, too, and will tolerate higher speed here. They are great for turning the insides of goblets, eggcups, and scoops. However, I do not find them any more efficient than a spindle gouge ground to a long fingernail and turned 45° to the left. With either a spindle gouge or a hook, you present the tool at the center, lever it sidewise, and drag it up the wall of the goblet or cup.
Ring tools are essentially the same as hook tools, but they lend themselves better to modern manufacturing methods. The ring may be turned on a screw machine and the handle spot-welded or mechanically fastened. Smaller rings are often investment cast. The one drawback to small ring tools over true hooks is that chips do not always clear through the ring well, thus the tool stops cutting due to chip backup.
Hooks and ring tools are best sharpened with a small grinding wheel mounted in a Dremel tool. Grind only the inside surfaces of the ring or hook.