Door/window terminology — vertical member through the middle of a shutter frame In joinery, what is the vertical member running through the middle of a window or door shutter frame called?

Introduction / Context:
Understanding joinery terms is essential for detailing, procurement, and site communication. A shutter (door or window) comprises vertical and horizontal members that hold panels or glazing. The correct identification of these members avoids mistakes in fabrication and installation.

Given Data / Assumptions:

• The question refers to a vertical member located within the middle of the shutter width.
• Standard door/window shutter components are considered.
• Conventional nomenclature is used.

Concept / Approach:
Stiles are the vertical outermost members at the edges of a shutter. Rails are the horizontal members (top, lock, bottom). A mullion is a vertical intermediate member that divides a shutter or window into multiple panels or lights. A reveal is the side face of a wall opening, not a part of the shutter frame; “post” is a general structural term not specific to shutter construction.

Step-by-Step Solution:

Verification / Alternative check:
Standard joinery drawings label vertical internal divisions as mullions and horizontal divisions as transoms.

Why Other Options Are Wrong:

• style (stile): edge vertical member, not middle.
• reveal: masonry/finishing term, not a shutter member.
• post: generic; does not denote the shutter’s middle vertical member.
• none of these: incorrect as “mullion” is correct.

Common Pitfalls:
Spelling confusion between “stile” and “style”; mixing up mullions with transoms (which are horizontal).

Final Answer:
mullion