Eyelash thickness

[Sarah L F]

hi there I’m new to lash extensions and I’m building my kit. I’ve been ordering Dolce Doll lashes and find them really good qauility. Can anyone recommend what is the most common thickness to be using on a client. I was taught to use 20 but not sure when bulk buying if that’s what I should be stocking up on and if that’s what most lash technicians use. Any help would appreciated. X