Gladiator 4-Tier Welded Steel Garage Storage Shelving Unit (77 in. W x 72 in. H x 24 in. D)

4 (four) is a number, numeral and digit. It is the natural number following 3 and preceding 5.

4 is the smallest square number > 1, the smallest semiprime and composite number, and the 3rd highly composite number.

The number 4 is considered unlucky in many East Asian cultures.

72 may refer to:

• 72 (number)
• One of the years 72 BC, AD 72, 1972, 2072
• "72", by James from the album Hey Ma
• 72 Feronia, a main-belt asteroid
• Tatra 72, an army off-road truck
• Audi 72, a compact executive car

77 may refer to:

• 77 (number)
• one of the years 77 BC, AD 77, 1977, 2077
• 77 Frigga, a main-belt asteroid
• Book 77, the Rights of Man
• Tatra 77, a sedan

D, or d, is the fourth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is dee (pronounced ), plural dees.

A garage is a covered structure built for the purpose of parking, storing, protecting, maintaining, and/or repairing vehicles. Specific applications include:

• Garage (residential), a building or part of a building for storing one or more vehicles
• Automobile repair shop, also called a garage, where vehicles are serviced and repaired
• Bus garage, a building or complex used for storage of buses when not in use
• Filling station, an automotive service station where vehicles take on fuel or recharge
• Multistorey car park, or parking garage, a building serving as a public parking facility

Other meanings of garage may include:

A gladiator (Latin: gladiator 'swordsman', from Latin gladius 'sword') was an armed combatant who entertained audiences in the Roman Republic and Roman Empire in violent confrontations with other gladiators, wild animals, and condemned criminals. Some gladiators were volunteers who risked their lives and their legal and social standing by appearing in the arena. Most were despised as slaves, schooled under harsh conditions, socially marginalized, and segregated even in death.

Irrespective of their origin, gladiators offered spectators an example of Rome's martial ethics and, in fighting or dying well, they could inspire admiration and popular acclaim. They were celebrated in high and low art, and their value as entertainers was commemorated in precious and commonplace objects throughout the Roman world.

The origin of gladiatorial combat is open to debate. There is evidence of it in funeral rites during the Punic Wars of the 3rd century BC, and thereafter it rapidly became an essential feature of politics and social life in the Roman world. Its popularity led to its use in ever more lavish and costly games.

The gladiator games lasted for nearly a thousand years, reaching their peak between the 1st century BC and the 2nd century AD.

H, or h, is the eighth letter of the Latin alphabet, used in the modern English alphabet, including the alphabets of other western European languages and others worldwide. Its name in English is aitch (pronounced , plural aitches), or regionally haitch , plural haitches.

Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron. Because of its high tensile strength and low cost, steel is one of the most commonly manufactured materials in the world. Steel is used in buildings, as concrete reinforcing rods, in bridges, infrastructure, tools, ships, trains, cars, bicycles, machines, electrical appliances, furniture, and weapons.

Iron is always the main element in steel, but many other elements may be present or added. Stainless steels, which are resistant to corrosion and oxidation, typically need an additional 11% chromium.

Iron is the base metal of steel. Depending on the temperature, it can take two crystalline forms (allotropic forms): body-centred cubic and face-centred cubic. The interaction of the allotropes of iron with the alloying elements, primarily carbon, gives steel and cast iron their range of unique properties. In pure iron, the crystal structure has relatively little resistance to the iron atoms slipping past one another, and so pure iron is quite ductile, or soft and easily formed. In steel, small amounts of carbon, other elements, and inclusions within the iron act as hardening agents that prevent the movement of dislocations.

The carbon in typical steel alloys may contribute up to 2.14% of its weight. Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel (either as solute elements, or as precipitated phases), impedes the movement of the dislocations that make pure iron ductile, and thus controls and enhances its qualities. These qualities include the hardness, quenching behaviour, need for annealing, tempering behaviour, yield strength, and tensile strength of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing iron's ductility.

Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in the 17th century, with the introduction of the blast furnace and production of crucible steel. This was followed by the Bessemer process in England in the mid-19th century, and then by the open-hearth furnace. With the invention of the Bessemer process, a new era of mass-produced steel began. Mild steel replaced wrought iron. The German states were the major steel producers in Europe in the 19th century. American steel production was centred in Pittsburgh, Bethlehem, Pennsylvania, and Cleveland until the late 20th century. Currently, world steel production is centered in China, which produced 54% of the world's steel in 2023.

Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering the cost of production and increasing the quality of the final product. Today more than 1.6 billion tons of steel is produced annually. Modern steel is generally identified by various grades defined by assorted standards organizations. The modern steel industry is one of the largest manufacturing industries in the world, but also one of the most energy and greenhouse gas emission intense industries, contributing 8% of global emissions. However, steel is also very reusable: it is one of the world's most-recycled materials, with a recycling rate of over 60% globally.

W, or w, is the twenty-third letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is double-u, plural double-ues.

X, or x, is the twenty-fourth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ex (pronounced ), plural exes.