M is for muntin; not to be confused with mullion or mutton. Muntins are the strips of wood or metal that divide window and door glass into a grid or geometric pattern. The width of muntins has varied over the years based on advancements in the manufacture of glass as well as the preferred window style and design standard of the time. Most residential windows have muntins ranging from one half to one inch wide.
Small panes of glass with wide muntins were prevalent in colonial architecture due to the limitations of glass blowing techniques and window sash production. To read the full on-line article from LNP News CLICK HERE.