Mullion

A vertical member separating and supporting adjacent door panels, sidelights, or glass lites within a frame assembly. Mullions divide wide openings into smaller sections while providing structural support and hardware mounting.

Removable mullions allow occasional full-width access for moving furniture or equipment. Keyed removable mullions secure with barrel bolts at head and floor; automatic flush bolts engage when the inactive door closes. Fixed mullions are welded or mechanically fastened in place permanently.

Mullion widths typically range from 1-3/4″ to 4″, depending on structural requirements and fire rating. Fire-rated mullions must be tested as part of the complete assembly and may require larger profiles for 90-minute ratings. Steel, aluminum, and wood mullions are available for different applications. Related terms: astragal, stile, sidelight. Browse frame options.

Since 1938, American Doors has supplied commercial doors, frames, and hardware across the U.S., growing from a Houston-based distributor into a multi-market platform serving contractors throughout Texas and Colorado. Family-owned for more than 85 years, we emphasize continuity and craftsmanship, with AHC-certified hardware specialists and experienced estimators delivering fully coordinated Division 8 and Division 10 solutions from specification through installation.

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American Doors is part of Riverbend Industries, a family-owned industrial group focused on building durable, operating businesses.

Riverbend partners with management teams for the long term—investing in people, systems, and manufacturing capability while preserving the culture and accountability that make each business successful.

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