On an exterior double door arrangement like the one above, an astragal covers the seam between the two door panels and is fitted with weather-stripping to prevent wind and water from entering the house.
A transom is a narrow window located above a door or window. Most transom windows do not operate, but if they do, they are typically hinged at the top like an awning window.
Simulated divided lite bars (SDL)
Because large panes of glass are now stronger, less expensive to manufacture, and more energy efficient
, muntin bars have largely been replaced with SDL Bars
which rest on the surface of the glass.
Grilles are bars that create the effect of divided lites but are removable for easy glass cleaning. Grilles-Between-the-Glass (GBG) are also available. As the name suggests, GBGs are bars that are permanently installed between the glass panes for easy cleaning and low maintenance.
Up to the middle of the 19th century, large panes of glass were fragile and expensive to create, muntin bars were joined together in order to create large expanses of glass from smaller individual panes (Not shown).