The CRL Nylon Combination Roller has a round edge roller on one end for creasing the screen cloth into the spline groove, and a concave edged roller on the opposite end for inserting the spline and screen into the screen frame spline groove. It has two nylon wheels which roll smoothly on steel ball bearings, and won't cut or tear the screen wire or spline. The contoured handle allows for a comfortable grip, which helps alleviate fatigue. This tool is an excellent choice for rolling fiberglass screen.