Professional Screening Tool & Retractable Knife Combo - This easy-to-use ergonomic tool is designed to reduce hand fatigue and provide professional results. The interchangeable rollers allow you to roll 17 plus styles of spline including, round, square, flat, star, Y, V, and more with ease. The knife is a quick change setup with locking feature, again utilizes the ergonomic design to reduce hand fatigue. The 3 included wheels are all sealed bearings, and can be changed out quickly. If you''ve ever spent anytime screening or re-screening, you understand the importance of have a good tool that provides professional results without damaging the screen. The wheels are specifically designed for the shape of spline you are rolling. This feature helps prevent the roller from rolling off the spline and cutting the screen you just replaced. This tool is not a cheap one time use tool, this tool is designed to last a lifetime and be part of your toolbox. The light weight, high impact body is designed to be virtually indestructible. If you purchased a quality knife and roller together, you''ll save money by purchasing this quality 2n1 tool.