Window Parts: Learn About the Components of a Window

Are you shopping for new windows, or is there a window in your home that needs repairing? This comprehensive window parts glossary is a great place to start.

July 13, 2022
Replacing the tired, leaky windows in your home with highly efficient Marvin windows can reduce your energy bills and bring more comfort to your favorite spaces. New Marvin windows can be designed to perfectly complement your home’s current architectural style or enhance an ambitious design transformation. To help you on your window buying or repair journey, here is a helpful guide that describes the various window components and explains their functions.

Window Components


Glazing is just another word for the glass in a door or window. The glazing in modern windows is 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 window or reflected away from it. Glazing can be enhanced with tints and laminations in order to add privacy, provide decorative options, and increase strength. Find out more about glazing.

Daylight Opening

The daylight opening (DLO) refers to the total amount of glass in a window not including the sash stiles and rails or the window frame.


The part of the window that holds the glass and opens and closes is called the sash. Window sashes and frames can be made out of several different kinds of materials including wood, aluminum, fiberglass, composite, and vinyl.


Stiles are the vertical window components of a sash.


Rails are the horizontal window components of a sash. The two rails that meet in the middle of double hung and single hung windows are called check rails.

Storm Sash

A storm sash is a separate sash constructed of very small stiles and rails. Storm sashes are not typically installed in the factory but are added to existing windows, usually single-pane windows, to help improve energy efficiency and comfort levels, especially during the cold winter months. Some storm sashes open and close while others are stationary, and they may be removed seasonally or left in place year-round. The use of storm sashes is not necessary on modern, highly efficient windows (Not Shown)

Direct Glazed

Some picture, or non-operating windows have no sash at all. These are called direct glazed windows. The glass on a direct glazed window is secured directly into the frame. The absence of stiles and rails creates a larger daylight opening and unobstructed view. The narrow and sleek aesthetic of direct glazed windows makes them more popular with modern architectural styles and in commercial applications (Not shown).

Sash Tilt Pin

The mechanism that allows sashes on double hung and single hung windows to tilt in for easy cleaning is called the sash tilt pin or sometimes referred to as a cam pivot.

Parts of a Window Frame

The stationary components of a window that enclose either the sash on an operating window or the glass on a direct glazed window are called the frame. Jambs, sills, and moldings are the primary components of a window frame. Narrow frame windows are available for a more modern aesthetic and are a popular choice when replacing existing windows.

Head Jamb

The head jamb is the top component of the frame.

Side Jamb

Side jambs are the vertical components of the frame.


The sill is the bottom component of the frame. The outside edge of the exterior portion of a window sill is tapered down to help shed water.

Jamb Liner

Jamb liners span the distance and cover the space between the window frame and the finished interior wall. Jamb liners are typically made of wood and can be installed at the factory or on site. Plaster or drywall is sometimes applied directly up to the window frame, which eliminates the need for jamb liners (Not shown).

Jamb Extension

Jamb extensions are thin strips of wood installed to the edge of a jamb liner in those cases when the jamb liner is not quite wide enough to line up with the finished surface of the wall (Not Shown).

Operating Handle

The operating handle on a casement or awning window is the mechanism used to open and close the sash. The type of operating handle shown here is called a crank handle. Turning the crank in one direction extends the operating arm and opens the sash, and turning the crank in the other direction retracts the arm and closes the sash. This handle folds down when not in use. Some casement, awning and hopper windows have non-crank handles used to simply push the window open and close it manually.

Operating Arm

An operating arm is attached to both the window frame and the sash on casement, awning, and hopper windows. It is the mechanism that works in conjunction with an operating handle to open and close a sash. It also holds a sash in position when open.

Locking Handle

The handle or lever operated lock found on a variety of window types is called the locking handle. When pushed closed, locking handles are designed to pull the two sashes tight together for improved security and energy efficiency.

Cam Lock

A cam lock is a rotating type lock found on a variety of window types. When turned closed, cam locks are designed to pull the two sashes tight together for improved security and energy efficiency. Lift Lock is a modern alternative to the traditional cam locking system for double hung and single hung windows.


A keeper is the stationary half of a cam lock.

Muntin Bars

Up until the middle of the 19th century, large panes of glass were fragile and expensive to create, so muntin bars were joined together in order to create large expanses of glass from smaller individual panes. When historical accuracy is important, windows can still be made with muntin bars or sometime referred to as authentic divided lite (ADL) (Not shown).

Simulated Divided Lite Bars

Because large panes of glass are now stronger, less expensive to manufacture, and more energy efficient, muntin bars have largely been replaced with Simulated Divided Lite bars (SDL), which rest on the surface of the glass.

Spacer Bars

Spacer bars can be installed between two pieces of glass at the same location as the simulated divided light bars. Spacer bars help to replicate the look and feel of authentic divided lite.


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 decorative bars that are permanently installed between the glass panes for easy cleaning and low maintenance (Not shown).


Window and door casing trim is designed to hide the gaps between a window or door frame and the surface of the interior wall. It is installed to the jamb liner and the finished surface of the wall. Casing is usually installed by a finish carpenter on site.

Brick Mould Casing

Brick mould casing, or brick moulding, is an exterior 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 moulding is often, but not always, installed at the factory (Not shown).


Screens are a see-through, tightly woven mesh most often made of either metal or fiberglass. Screens block out insects and debris like airborne seeds and falling leaves yet still allow light and air to enter the home. Some screens are installed into a narrow frame that can be removed for cleaning.

Sash Limiter

A sash limiter is an optional device that can be set to limit the distance a window sash will open, but these devices are not designed to meet code requirements as Window Opening Control Devices are (Not shown).

Triple Pane

Many windows can be built with three panes of glass instead of two. Like standard dual pane glass, the space between the panes is insulated with argon gas, and a variety of Low E coatings can be applied to the glass surfaces to achieve a variety of performance requirements. Triple pane glass is sometimes chosen to increase energy efficiency in extremely harsh climates or as a noise mitigation solution.

Glass Spacer

Individual panes of glass are separated by glass spacers. These spacers also prevent the gas insulation from escaping.

Stop Moulding

Blind stop, parting stop, and sash stop are common types of stop mouldings found on a window. The function of most stop mouldings is to keep sashes secure and aligned within the window frame.


For Marvin products, cladding refers to the colored extruded aluminum used to cover the exterior portions of wood sashes and frames. Window and door cladding combine a low maintenance and durable finish of aluminum with the stability and insulating properties of wood.

Glazing Bead

The strips of profiled wood, vinyl, or capped aluminum used to hold the glass in position within the sash are called glazing bead. Glazing bead on the interior side of the sash is often called sticking. Ogee and Ovolo glazing bead offer a more traditional profile, and square beads are available for a clean, more contemporary look (Ogee shown).


Weather-stripping helps seal the gaps between the various components of a window sash and frame. In the past, weather stripping may have been made of a malleable metal like brass, but modern weather-stripping is typically made of a resilient, flexible material like silicone, rubber, vinyl, or foam.


When two or more windows are connected to each other, the area where the two side jambs meet is called a mullion (Not shown).

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