How-To

Parts of a Door: Learn About the Anatomy of a Door

Are you shopping for a new door, or is there a door in your home that needs repairing? You could benefit from this door parts glossary.

If you’re embarking on a door replacement or new build project and you’re overwhelmed with all the technical terms, we’ve got you covered. This post breaks down all the parts of a door so you can understand the terminology and how all the parts and pieces come together. Understanding the basic parts of a door makes it easier to talk with contractors and dealers to choose the right door for your project.

Figure 1. Shows Door Parts including: Head Jamb, Side Jamb, Casing, Mullion (Mull), Threshold, Sidelight and Glazing.

Door frame

Side jambs, head jambs, and mulls are the parts that make up the frame. Residential door frames are most often made of wood but can also be made of aluminum, fiberglass, or a composite material. Door frames can be purchased primed (ready to paint) or ordered with a factory finish in a variety of colors.

Head jamb

The top horizontal section of a door or window frame is called the head jamb.

Door jamb versus door frame

A door jamb is an individual section of a door frame. Two side jambs make up the vertical components of the door frame and the head jamb is the top horizontal component. Together, the jambs (along with mullion) comprise the door frame.

Mullion (mull)

When two individual windows or a door and window are joined, the seam between the frames of the two units is called the mull, which is short for mullion. In this case, a door jamb has been joined to a window/sidelight jamb. The seam is typically hidden with a piece of trim called a mull casing (See additional definition below).

Sill

Sills are the bottom component of a door frame. They are the part of the door that gets sealed and fastened to the floor. Only exterior doors (those that lead to the outdoors or garages) have sills.

Threshold

A threshold is the protective cap that covers the sill. It is typically sloped toward the outside to help shed water. Thresholds are made of durable materials like metal or fiberglass because they need to be strong enough to withstand foot traffic.

Glazing

Glazing is just another word for the glass in a door or window. The glazing in newer exterior doors like this one are made up of at least two layers of glass and sometimes three. Inert gas, usually argon, is injected between the glass layers to provide additional insulation. Nearly invisible coatings are added to glass to help manage the amount of light and heat conducted through a windowpane or reflected away from it. Glazing can be enhanced with tints and laminations in order to add privacy, provide decorative options, and increase strength.

Sidelights

Sidelights are tall narrow windows found on one or both sides of a door. Sidelights allow more light into entryways, improve views, and can create a more welcoming entry point experience.

Casing

Window and door casing trim is designed to hide the gaps between a window or door frame and the surface of the interior wall.

Figure 2. Shows Brick Mould and Weatherstripping

Brick mould

Brick mould is an exterior casing trim designed to conceal the gap between a window or door frame and the exterior wall surface. Brick mould is thicker than most interior casing trim profiles and provides a buffer between the window/door and the brick or other cladding surrounding it. Brick mould can be made of wood, aluminum, PVC, fiberglass, or composite materials and is the part of the door that a screen door or storm door is attached to.

Weatherstripping

On exterior doors, weather-stripping helps seal the gaps between a door frame and a closed-door panel, weather-stripping is typically made of a resilient, flexible material like silicone, rubber, or foam.

Door sweep (not shown)

The weather-stripping installed on the bottom of a door panel, a door sweep creates a weather resistant barrier between a door panel and sill.

Figure 3. Shows Transom, SDL Bars and Astragal

Astragal

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.

Transom

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 (not shown)

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.

Muntin bars (not shown)

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).

Diagram of an interior door and its parts.

Figure 4. Shows Top Rail, Panel, Lock Stile, Bore Hole, Mullion, Bottom Rail, Stop Moulding, Hinge Style, Mid Rail, Hinge

Panel

A door panel, sometimes called a slab, refers to the whole part of the door that swings back and forth. Full door panels are often divided up into smaller panels, which are set between the stiles, rails, and mullions.

Rail

The narrow horizontal segments on a door panel are called rails. This door has a top, bottom, and a mid-rail.

Stile

A stile is the narrow vertical segment located on either side of a door panel. One is called the lock stile and the other a hinge stile.

Mullion

A mullion resembles a stile. It is the vertical component that separates two panels located in the middle of the door between the rails.

Stop moulding

Door stop moulding is attached to a door frame. It aligns the door panel within the frame and prevents the panel from swinging right through the opening.

Hinge

This is the piece of hardware that allows the door to swing open and closed. Standard sized doors have three hinges, but larger doors will have four or more. The color or finish of the hinges typically matches the finish of the lockset.

Bore hole

A bore hole is drilled into a door to accommodate a lockset.

Lockset

The lockset refers to the handles, locks, latches, strike plates, and all the other hardware components that allow a door to latch and lock in place. Locksets are also referred to as handlesets or hardware.

Handle

A handle, knob, or lever is the component of door hardware that is used to unlatch the door panel and pull it open or push it closed. There are many styles and finishes to choose from. There are three types of door handles:

Entry handles are operated with a key cylinder on the exterior side of the door and a push or turn lock button on the interior.
Bed/bath handles have a push or turn lock button on the inside but not on the other.
Passage handles have no locking mechanism.

Latch

A door latch is a shaft that protrudes from the edge of a door panel and into the door frame securing the panel in place. When the handle is turned, the latch retracts allowing the door to be opened.

Deadbolt

Similar to a latch, a deadbolt is a shaft that protrudes from the edge of the door panel and into the door frame securing the panel in place. Residential interior doors are not equipped with deadbolts, and not all exterior doors have them either. Deadbolts are considered an additional form of security and are most often set apart from the handle assembly, which means that a door with a deadbolt needs an additional bore hole. Multi-point locking hardware systems provide even more protection than a latch and deadbolt combination, and new home automation systems are available.

Thumb turn

A deadbolt is operated by turning a thumb turn on the inside of a house and by a key cylinder on the exterior side.

Mortise plates

These plates add strength to latches, deadbolts, and the door panel, which helps prevent a forced entry.

Strike plates

Strike plates add strength to door frames which helps prevent a forced entry.

Escutcheon

Escutcheons are ornamental plates that can be found surrounding handles, thumb turns and key cylinders. They’re designed to protect the surface of the door panels from nicks and scratches.

Grilles (not shown)

Muntin bars (not shown)

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