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(863) 293-2977

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Glossary of Window & Door Terms

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Argon Gas

A colorless and odorless gas used to fill the airspace between insulating Low E glass. The addition of argon greatly increases the insulating performance of the Low E glass.


Single units mulled together.


A moulding applied to one stile of a French Door, Sliding French Door or French Casement window unit which the other door panel or window sash strikes. Usually head and footbolt devices will be found on the astragal side.

Authentic Divided Lites (ADL)

Also known as True Divided Lite. Permanent stationary muntins and bars separate the glass in a window or door sash to give the sash two or more lites of glass.

Awning Window Unit

A combination of frame and sash, hinged at the top of the vertical jambs which allows the unit to pivot from the top with the sash opening to the exterior of the building


A block and tackle system used in the jamb liner of double hung or single hung units.

Bay Window

A series of windows installed in a bay which is two flanker units and a center sash; a bay may be an arc or a polygon; when a bay is or closely approaches an arc, the window is termed a bow.  See Bow Windows.


The frame member on a double hung window located between the jambs and the casing. The blindstop forms a rabbet that supports either a storm sash or screen.

Bow Window

A series of adjoining window units, installed on a radius.

Brick Mould Casing (BMC)

An exterior moulding of window and door frames that abuts the exterior facing material of the structure. The casing serves as the boundary moulding for brick or other siding material and also helps to form a rabbet for screens and/or storm sash or a combination door.

Cam Pivot

A zinc pivot pin attached to the top and bottom sash stiles of double hung units (bottom sash on single hung units). Cam pivots rest on the clutch system of the balance tube assembly which allow opening and closing of the sash.

Casement Window

A combination of frame, sash, weather-strip, concealed hinges and operating device assembled as a complete and properly operating unit. Casements have a flat sill and a sub-sill; screens and/or energy panels are optional. Operating casements have a crank handle for smooth operation.


The plastic and metal assembly on which the cam pivots of a double hung or single hung sash rest. The clutch is attached to the block and tackle system of the balance tubes which allow opening and closing of the sash. The clutches are color coded for easy identification of balance strength.

Combination Storm

A wood or aluminum storm sash with self-storing screen and operating glass panels. Available for double hungs, gliders and wood swinging doors, these panels are removable.

Combination Window

A wood or clad wood frame storm sash with self-storing screen. Bottom glass panels such as those installed on a double hung unit operate by moving the plungers in and sliding the glass panel up to the desired position. Side glass panels such as those installed on gliders slide to the left or right to the desired position. All inserts are removable from the inside.

Cottage Window

A window with unequal sash, top and bottom.

Daylight Opening

The width and the height of the visible glass.

Double Hung

Double hung windows have two movable sash which operate vertically. Double hung sash are held in an open position with the use of coil spring block and tackle balancing devices.

Drip Cap

A formed aluminum or vinyl piece which is installed at the top of windows and doors that allows water to run off the casing of the unit instead of seeping around the casing and into the unit.

Energy Panel (EP)

Formerly called an RDG – removable double glazing, is a piece of glass annealed or tempered, and finished on the edges by a surround. EPs are applied to windows or doors and rest on the glazing stop. EPs offer the homeowner added energy efficiency.


An article or product of vinyl or metal-made by the process of extruding. Extrusions include vinyl sill and head jamb tracks, vinyl jamb liners and aluminum cladding used on the exterior of clad units.

Finger Joint

A series of fingers machined into the ends of two pieces of lumber to be joined together. They are then held firmly in position by adhesive. Finger jointed wood is very strong and has a lesser chance of warping than does a clear piece of wood the same length.

Flat Casing

Flat, surfaced on four sides, pieces of pine of various widths and thicknesses for trimming door and window openings. The casing serves as the boundary moulding for siding material and also helps to form a rabbet for screens and/or storm sash or combination doors.


A locking rod device installed vertically in the stile or astragal of a door or screen which when activated secures the panel or screen in a stationary position.


The stationary portion of a window that encloses either the glass (direct glaze) or the sash (operating or stationary) and consists of the head jamb (top), sill (bottom), sub-sill, side jambs, jamb extension, brick mould or flat casing, and blindstop.

Frame Expander

A flat aluminum extrusion used in conjunction with the 90 degree frame expander to provide a flat casing appearance for clad units.

French Casement

A casement styled unit with two sash in one frame providing a sense of openness unrestricted by a vertical mullion or stiles when both sash are open.

Glass Size (GS)

The measurement of the actual glass, not the visible glass.


Installing glass into windows and doors.

SINGLE GLASS: Glazing with a single piece of glass.

INSULATING GLASS: two panes of glass separated by a spacer and hermetically sealed together with dead air space between the panes.

Glazing Bead

Strips of profiled wood or vinyl used to hold the glass in position in the sash. Wood glazing bead is attached to the rails and stiles of the sash using staples, small nails or vinyl barbs. A vinyl bead is held in place by extruded barbs positioned in the kerf. Aluminum caps may be used over the vinyl bead in some cases.

Glazing Tape

A two sided adhesive tape placed between the glass rabbet and the glass and/or the glazing bead and glass of some unit types.


Horizontal operating units which have one sash fixed while the other glides open and shut horizontally.


A term used to describe the right or left hand operation of a window or door.


A locking rod device installed vertically in the stile or astragal of a door or screen which when activated secures the door in a stationary position.


A term used to define a window or door product meeting the requirements of historical renovation standards.

Insulating Glass (IG)

(See Glazing)

Inswing French Door

A French door with panels that swing to the inside. One, two, three and four panel units available as stationary or operating.

Interior Casing

The casing trim used on the interior perimeter of the window or door. Generally supplied by others except in the case of round top casing which is factory supplied.

Jamb Extension

A jamb-like member, usually surfaced on four sides, which increases or extends the depth of the exterior or interior window or door frame; jamb extensions imply a larger depth than “wood jamb liners.”

Krypton Gas

Inert gas known for its ability to provide insulating properties in a small air space.

Laminated Glass

Glass composed of two sheets of glass fused together with a sheet of transparent plastic between the sheets. When broken laminated glass will generally not leave the opening.


A method of gluing strips of thin clear wood to the lengthwise surfaces of finger jointed material to provide the appearance of clear stock.

Lever Lock

A lever handle and lever arm operator available as an option on awning units.

Low E Glass

Low E stands for low emissivity. The lower the emissivity the higher the percentage of long-wave radiation blocked thereby improving thermal performance.

Low E glass is coated with a thin microscopic, virtually invisible, metal or metallic oxide layer. The primary function is to reduce the U-value by suppressing radiative heat flow. A secondary feature is the blocking of short wave radiation to impede heat gain. There are two basic types of Low E glass. The first, vacuum or sputter coated Low E, is referred to as soft-coat (See Low E II definition). The second is pyrolytic Low E, commonly referred to as hard-coat. (See pyrolytic definition.)

Low E II Glass

A high performance Low E glass, providing the best winter U-value and warmest center glass. It offers significant improvement in reducing solar heat gain coefficient values, providing customers one of the coolest summer glass temperatures of all Low E products.

Additionally, ultraviolet light transmission is greatly reduced. The Low E II coated glass products are specifically designed for insulating glass units normally as a second surface coating.

See Low E and pyrolitic definitions.

Masonry Opening

A brick, stone or block opening into which a window or door unit is installed including the outside casing.


The act of attaching two or more window or door units together. The joint is then finished with a mullion center cap or mull trim.


The vertical member of a sash, window or door frame between openings in a multiple opening frame.

SPACE MULL: Two or more units mulled together with a space left between the units. The jamb extension surrounds the entire unit.

STUD POCKET: Two or more units mulled together with a space between the units. The jamb extension surrounds each unit separately, providing space for a support member between the units.

Mullion Reinforcement

The 3/8″ mullion reinforcement is designed to be used on wood or clad multiple casement, awning and direct glaze assemblies to improve structural performance.

Muntins (or "munt")

A short “bar,” horizontal or vertical, extending from a bar to a stile or rail or another bar.

Nailing Fin

A factory installed vinyl strip that is inserted into a kerf in the frame of clad units.

Nailing fin installation is the standard method used for installing clad units.

Obscure Glass

Glass formed by running molten glass through special rollers. These rollers have a pattern on them causing the glass to become patterned and thus obscure.

One-Wide (1W)

The current term used to describe one frame with single or multiple sash or panels.


An operating sash, panel or unit.


Outside Measurement.

OX or XO

The letters OX or XO identify the operation of window or door units as viewed from the exterior.

The letter O stands for stationary while the letter X stands for operating.


A term used to describe the angle of a roof. For example: A 4-12 pitch indicates that the roof rises 4″ vertically for each 12″ horizontally.

Pole Crank

An aluminum extension pole used to open or close roof windows or awnings which would be inaccessible because of their height.


Lineal profiles of constant cross section manufactured by combining plastic resin and continuous glass fiber reinforcement. These thermally insulating and structural components are ideally suited for applications where strength, thermal stability and weather resistance are required, such as in patio door frames and commercial windows.

Pyrolytic Low E Glass (Hardcoat)

Pyrolytic Low-E is designed to be used either in non-insulating applications such as energy panels that have exposed surfaces or for insulating glass applications.

In some northern climatic situations where an application or customer requires increased solar heat gain, over Low E II performance, this is a desirable option. This increased solar heat gain which is desirable in winter may increase summer energy costs if the home is air conditioned.

The pyrolytic coating is typically applied to the second surface, but can be applied to the third surface to provide increased solar heat gain.


A groove along or near the edge of a piece of wood.


The cross or horizontal members of the framework of a sash, door or other panel assembly.

Rough Opening

The opening in the wall where a window or door unit is to be installed. Openings are larger than the size of the unit to allow room for insulation and to shim the unit square.


The operating and/or stationary portion of the window unit that is separate from the frame. The sash consists of the following parts:

STILES: Vertical sash members.

RAILS: Horizontal sash members.

CHECK RAILS: Horizontal sash members that meet, as in double hung units. These could also be vertical check stiles, as in the glider or patio door.

BARS: Divisional members extending from rail to rail or from stile to stile in an authentic divided lite unit.

MUNTINS: Divisional members extending from a bar to a rail or stile or another bar.

Sash Opening (SO)

The opening between wood frame members for both height and width (disregarding any jamb hardware tracks). This measurement is used predominantly when measuring an opening for the Double Hung Tilt Pac.


A close-mesh woven screen material of metal or fiberglass attached to an aluminum or wood surround. Screens inhibit entry of insects, yet permit light, air and vision.


The horizontal member forming the bottom of a window or exterior door frame; the lowest member of the frame of a structure, resting on the foundation and supporting the frame.

Single Hung

A window very similar to a double hung window, except that the top sash is stationary or non-operable.


The upright or vertical perimeter pieces of a sash, panel or screen.


An attractive, protective trim which is secured to an energy panel by an adhesive or vinyl barb to give the glass panel a safe finished edge. Also the aluminum framework for most standard screens.

Tempered Glass

Float glass panels heated and then cooled rapidly in a controlled environment. This process makes the glass several times stronger than regular glass. It also makes it safer because when broken it yields small pebble-like fragments.


A window above a window or door. Transoms can be either stationary or operating.


A measure of total heat flow through a window or door barrier from room air to outside air. Lower numbers indicate greater insulating capabilities.

Wire Glass

Glass with wire embedded into the glass when the glass is still in a molten state. This prevents the glass from falling out of the sash if it should break.

Central Window Sales, Inc.