These pairs of window hinges are constructed of stainless steel mounting plates and steel link arms. The link arms are protected with a corrosive-resistant E-Gard coating and attach to the window sash. Once installed, these hinges are concealed from view from both the inside and the outside, but may require a special rabbet or plow for proper mounting onto the sash. These types of concealed window hinges can be used with crank-out and push-out casement windows, crank-out and push-out awnings windows, tilt-in hopper windows and transom windows. Set screws are not provided with these hinges, but when inserted into the plastic glides, they can convert to concealed friction hinges, commonly used on push-out casements to hold open when slightly windy, and with awning windows to prevent "bouncing" when closing. These hinges can be mounted at the header, on the sill or sides of the window openings. Installation fasteners are included with each pair. Use a #6-32 machine screw in the black plastic slider to cause friction to stop the window in place. A thumbscrew works best.