Large polycarbonate window so you can see your work. To install: slide the front piece straight on, then slide the back piece on and down. Designed and 3D Printed in the USA by a small business. This adapter has a large clear polycarbonate window. To install, push the front piece onto the router base, then push the back piece on and slide it down to lock the two together. To remove, do the steps in reverse. Slide the back piece up and off. This unlocks the front part, allowing you to slide it off. The polycarbonate window can be accessed by undoing the small screws at the top if you ever wish to replace it. If you have any questions, please let me know. 3D printed in the USA by a small business.