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A grille or grill (French word from Latin craticula, small grill) is an opening of several slits side by side in a wall or metal sheet or other barrier, usually to let air or water enter and/or leave but keep larger objects including people and animals in or out.
In the United States, "grille" is used to avoid confusion with the cooking device, called a "grill".
In powered vehicles 
In automotive engineering, a grille covers an opening in the body of a vehicle to allow air to enter. Most vehicles feature a grille at the front of the vehicle to protect the radiator and engine. Other common grille locations include below the front bumper, in front of the wheels (to cool the brakes), in the cowl for cabin ventilation, or on the rear deck lid (in rear engine vehicles).
Nowadays big grilles are primarily cosmetic. The grille is often a distinctive styling element, and many marques use it as their primary brand identifier. For example, Jeep has trademarked its seven-bar grille style.
Rolls-Royce is famous for arranging its grille bars by hand to ensure that they appear perfectly vertical. Other makers known for their grille styling include Bugatti's horse-collar, BMW's split kidney, Rover's chrome "teeth", Mitsubishi's forward swept, fighter aircraft-style grilles for their cars 2008 Lancer and Lancer Evo X, Dodge's cross bar, Alfa Romeo's six-bar shield, Volvo's slash bar, Audi's relatively new, so-called single-frame grille, Pontiac's split horizontal grille and an egg-crate grille on late-generation Plymouths. The unusual 1971 Plymouth Barracuda grille is known as a cheesegrater. Ford's three-bar grille, introduced on the 2006 Fusion, has become distinctive as well.
The contrary styling pattern also occurs. Starting from the late 1930s, Cadillac would alternate its pattern from horizontal bars to various patterns of crosshatching as a simple way of making the car look new from year to year, for this make did not have a standard grille form. Sometimes there is a sort of fashion trend in grille bars. For example, in the early years after World War II, many American car makers generally switched to fewer and thicker grille bars.
A billet grille is an aftermarket part that is used to enhance the style or function of the original OEM grille. They are generally made from billet, solid bar stock aircraft-grade aluminum, although some are CNC machined from one solid sheet of aluminum.
Customizers would alter the grille as a matter of course in personalizing their car, taking the grille bar from another make, for example. Even sheet metal with patterned holes for ventilation grating sold to homeowners for repair has been found filling the grille opening of custom cars.
Grille types 
Per mounting location on the car body:
- Radiator grille
- Bumper skirts grilles (front and rear);
- Fender grills (brakes ventilation duct covers);
- Hood scoop grill (allow intercooler air flow)
- Roof grilles or trunk grills (rear engine vehicles);
Per style 
The American aftermarket restyling industry defines two major grille styles:
- OEM factory-style grilles – Such grilles have no difference with those manufactured by the automobile producers;
- Custom style – produced in small quantities and have an assortment of materials.
Per fastening method 
- Bolt over style
In this installation method, the billet grille simply bolts over the existing OEM plastic grille. This method does not require drilling or cutting of the OEM grille shell. Hidden bolts, brackets and clamps are used for this simple installation. The downside is it may not look as clean as the replacement style, because you can still see the OEM grille underneath. Bolt overs should take no more than 30 minutes to install.
- Replacement style
The OEM grille must first be removed and then the replacement billet grille must be mounted in place of the OEM grille. Drilling and sometimes cutting is required for this method. Installation instructions are always provided by the grille manufacturer, but unless you are a handyman you will need to take this job to a professional garage.
Material types 
- ABS plastic grilles – The major part of the OEM Grilles is produced by casting ABS plastic with various admixtures, which bring in plasticity to this less expensive and often fragile material.
- Aluminum grilles – Because of the physical characteristics of the material, aluminum is widely used by manufacturers of the aftermarket car grilles. Aluminum is a lightweight, corrosion resistant, and durable metal with the color varying from dull gray to mirror silvery. The material is so malleable and ductile that the manufacturers can produce grilles of almost any shape.
- Stainless steel grilles – Stainless steel is 3 times more durable than aluminum: it is corrosion and stain resistant. These qualities as well as low maintenance make stainless steel grilles a competitive product. These grilles are perfect for the off-road driving as they provide better protection for your car's radiator.
Grille finishes 
- Chrome grilles are usually made of aluminum or stainless steel, which is highly polished to achieve sparkling finish. These can be covered with a layer of chrome to add silver accent. Manufacturers may also use ABS plastic as a base material.
- Powder coated grilles involve sputtering of special components over the raw metal grille to obtain grainy surface with graphite or matte effect. The sputtering may be based on heat treatment, magnetic rotation or other processes, depending on manufacturer.
- Custom finishes are created by each specific manufacturer and are not widely spread. For example, leopard finish features sports that are engraved over the whole grille to resemble the leopard's skin. There is a countless amount of custom finishes, which can't be divided and form a large class of grille finishes.
- Painted grilles are the subtype of the above mentioned ones. Depending on the model, either frame or mesh is painted. The mesh usually has the same color as the car's body, while the frame is in contrast with the main color. The number of color variants is limited by the designer's fantasy only.
Grille Patterns 
- Billet grilles - are made from Aluminum. Billet grilles have a high-luster polished or chromed front face with a black baked on powder coating finish back ground.
- Mesh grilles - This grille type usually used in fast cars, made of stainless steel woven mesh, Electro polished to a high-luster finish or zinc plated, then finished with baked on powder coating. For steel to be considered stainless, it needs to have at least a 10.5% chromium content. There are two types of steel used in mesh grilles, 409 series and 304 series stainless steel. The 304 series has a higher chromium content and is more durable and more resistant to corrosion.
Grilles on automobiles have taken on different designs through the years. This feature first appeared on automobiles in 1903. Several years later, the arch-shaped design became common and became the standard design on automobile grilles for many years. The "split" grille design first appeared in 1923 on the Alfa Romeo sports car.
In the 1930s and 1940s, automobile manufacturers became creative with their grille designs. Some of these designs were bell-shaped (Buick, Chevrolet, and Pontiac), split and slightly folded (Silver Arrow, Mercury, 1946 Oldsmobile), cross-shaped (pre-war Studebaker Champion models, 1941 Cadillac, 1942 Ford), while some including Packard, Rolls-Royce, and MG-TC models still followed the older arch-shaped design.
In heating and ventilating and air conditioning 
In heating and ventilating and air conditioning for room air distribution, a grille, specifically spelled with the ending e, is a class of air terminals. Most HVAC grilles are used as return or exhaust air inlets to ducts, but some are used as supply air outlets. Diffusers and nozzles, are, for example, used as supply air outlets too. Registers are a type of HVAC grille that also incorporates an air damper.
See also 
- "Daimler Chrysler loses battle for injunction against GM H2 grille". 2002-11-18. Retrieved 2006-07-17.[dead link]
- Designer's Guide to Ceiling-Based Air Diffusion, ASHRAE, Inc., Atlanta, GA, USA, 2002
- ASHRAE Handbook: Fundamentals (SI Edition), 1997