Install the stem and handlebars as shown in the photos below. Using an Allen key fully tighten the handlebars as shown in photo 3 below. Now close the lever on the stem as shown in photo 4 below. The lever should be hard to close. If it closes very easily, it won’t fix the handlebars tightly. If the lever closes very easily or if it is too stiff to close, you can adjust its tightness, by tightening or loosening the bolt highlighted in photo 6, below