The small hooks on the Knit and Purl Tool are best used with lighter weight yarns such as sock yarns that are rated as 1, 2, and 3. The best looms to use the smaller hooks are sock or rectangle looms with the slider ends, looms with smaller pegs, such as some of the CinDwood Looms, Cottage Looms, Noble Knitter Looms (looms that use cotter pins), Martha Stewart Looms (small pegs) and Kiss Looms. Although looms with regular sized pegs can be used with the smaller hooks as well, especially if you are using a lighter weight yarn.
The medium sized hooks work well with heavier weight yarns and looms with an average sized pegs. Even some bulky weight yarns can be used with the medium sized hooks of the Knit and Purl Tool, just as long as the yarn has a tighter weave to it. Looms that work well with the medium sized hooks are CinDwood Looms (standard peg size), Knifty Knitter style looms, looms that are gauge adjustable such as Knit UK Looms, and Martha Stewart Looms (larger pegs).