Term:Mullion

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A mullion is a vertical or horizontal bracket or member that is designed to provide intermediate support to a structure or frame. A mullion has different applications within construction, below are a few examples:

  • Window Mullion – an intermediate member on curtainwall or a window which provides support for the glass. These are often found where two glass panes terminate and additional support is required.
  • Door Mullion – these are often found in the middle of a double door. Their job is to support the door frame to avoid sagging in the header.

Mullions are traditionally made of aluminum, wood or steel.

Merriam-Webster Online Dictionary
mullion (noun)
a slender vertical member that forms a division between units of a window, door, or screen or is used decoratively