It uses to peel 250um coating of 125um fiber optic,1.98mm open pore at the top uses to peel protective covering of fiber optic pigtail. After manufacturers preset all of sizes, you do not need to adjust .All of cutting ends has precise mechanical tolerance to make operation clean and smooth. Handset is designed by human engineering theory,so you will feel comfortable when grasping.Please make pliers in the closed position if you don't use it.