Flat Vs Contoured Grids . Yeah i did ask him about the pricing. The clearance between the glass for internal grids is one major consideration when choosing your window grid profile. Window Replacement Window Installation Comfort Windows from www.comfortwindows.com The clearance between the glass for internal grids is one major consideration when choosing your window grid profile. The difference between the two types of burrs is the shape of their rings. These grids are placed between the panes of glass, so the surfaces of the pane are easy to clean.