What does the number of teeth mean for thinners?
Teeth size, spacing and blade length all effect the finish a thinner gives the coat. As a general rule, more teeth means a smoother more even result. However, if 2 thinners both have 48 teeth, but one thinner is 8" long and the other is 6" long, the difference in scissor length means the teeth spacing will be different.
You'll get a more even, smoother result if the teeth are small and spacing between the teeth is small also, about the same spacing as the width of the teeth themselves. For a more natural, textured result, look for teeth that are larger than the spaces between them.
In blenders, which is a type of thinner with one notched and one solid blade, shorter with a high teeth count are popular - around the 6.5" length with 40+ teeth. In chunkers, also which have one notched blade and one solid blade, longer with fewer teeth are more popular - around 8.5" with 20+ teeth.