A glazing bar is a bar or stiff support strip that connects two panes of glass. Glazing bars are commonly featured in doors, windows, and furniture in western forms of architecture. Muntins are microscopic glass panes that split a single window sash or casement into a grid system. They are used where aesthetic quality is important, such as in windows for homes or shops. There are several types of glazing bars: pin-jointed, snap-jointed, and tongue-and-groove. Pin-jointed bars can be moved only horizontally, while snap-jointed bars can be rotated through 90 degrees either direction. Tongue-and-groove bars are designed to fit together with a lip and a groove on each piece. They cannot be separated easily; therefore, they are useful for connecting panels that will not be opened frequently. The term "glazing bar" also refers to the metal channel between the glass panes in a door or window frame. This channel holds the glazing bar insertion slots, which are usually located near the top of the frame for easy access by the installer. The term "glazing bar" does not refer to plastic channels or strips used instead. These items are called "edge bands" or "stiles". Door and window frames are made from various materials including wood, steel, and vinyl. Each type of material has its advantages and disadvantages.