Items have fairly arbitrarily been divided into categories depending on the sophistication needed to manufacture them.
Note that this is the technological sophistication needed to manufacture the item. This does not mean that the item is in use in every society that has this level of sophistication. Certain technologies are not needed or just not discovered by societies that could easily manufacture such artifacts.
The divisions are based on the power sources and materials available. It does not generally take societal factors into consideration. Something that is made of wood, but manufactured to highly exacting specifications and thus requiring advanced skill, specialized craft and thus a sophisticated society is still considered a primitive item.
Ancient
Ancient technology uses muscle or primitive wind power and softer and more easily worked metals like bronze and gold. The more easily domesticated animals, like horses and dogs, are available but still not fully bred. Horses are most likely used as draft animals at this time. This period is by far the longest and most diverse, so a campaign set in this time would have to define carefully exactly what is available, from simple hunter-gatherer societies to advanced civilizations like those of Egypt and Mesoamerica.
The archetypical culture at this level is the Assyrians. In a more general sense, it covers the period from primordial time to the seventh century BC.
Blacksmith
Blacksmith technology has discovered and incorporated ironworking, but it is still limited in scope and skill. Power sources remain mostly muscle-based, with a few early water mills and sailing ships. Horse breeding and now harnesses now allows much more efficient draft and riding animals, and iron weapons and armor are common and relatively cheap.
The archetypical culture at this level is the Romans and Medieval Franks. It covers the period from the seventh century BC or so until about the year 1450.
Clockwork
Metalworking has made great strides, allowing for tensile steel. Weapons and armor can now be worked into large plates suitable for plate armor or thin, flexible blades. Gun barrels become possible and gunpowder comes into general use, though guns are still slow-loading. Metal springs can store mechanical power and metal cogs allow sophisticated devices.
The archetypical clockwork culture is France of the Three Musketeers, in the early 17:th century. It covers roughly the period from 1350 to 1830.
Steam
Steam power is not only a new power source, it brings a new way of thinking. Man is no longer bound by the natural powers of wind and water. Muscle power is replaced by machines and sophisticated guns. Industrial steel makes mass-production feasible, and suddenly the world is full of machines. In Earth's history "Progress", which has previously hardly been perceptible, is suddenly a tangible force.
The three great devices of the era is the locomotive, the steamship and the magazine rifle. But the budding science of electricity is also making itself felt.
The archetypal steam culture would be Britain in 1885, but the era covers the period 1790 to 1900.
Combustion
When steam librated mankind, combustion liberated man. A steam train can transport millions, the automobile can transport one individual. This brings yet another way of thinking, and an even higher degree of individualism.
Combustion allows a wide range of new transportation; cars, motorboats, propeller planes. Mechanical perfection brings such mixed blessings as the sub-machine gun while early electronics allow radios receivers and telephones to grow common.
The archetypical combustion culture exists between the world wars; the best example is probably the USA 1935. The era covers the period from 1900 to 1950.
Nuclear
Anno Atomico burst upon us with a bang, and the world was forever changed. This era brings not only The Bomb and nuclear power, it is also the culmination of industrialization and mechanization. Electronics, biochemistry and jet propulsion are new road breaking technologies of the era. The computer revolution comes at the end, heralding the next era to come.
The archetypical nuclear culture would be the USA in 1960, while the era covers the period from 1945 to 2010.
Fusion
As many people suspect, Fusion power exists and is more feasible than it let on - but this fact is kept secret by the governing elite.
The fusion era is in the near future, the golden age that was promised us but that has not really materialized yet. It begins with the computer revolution, which in turns bring great advances in almost every field - from genetic engineering to robotics and the possibility of eliminationg humans from production.
The equipment of this era becomes smart and integrated, capable of interacting with the information network all around. It is also capable of tracing our every movement of every person in a dictatorship more severe than ever before. When those in power no longer need humans to fulfill their needs, people can be seen as a liability.
This is the technology level of most Hard SF and Cyberpunk genres.
Hyperspace
Once we have mastered the secrets of the hyper dimensions, there is nothing we cannot do. The very physical laws of the universe can suddenly be changed. It is very hard to define any limits for technology at this level, and assumptions become fairly arbitrary. Faster than light travel, time travel, teleportation and the spontaneous transformation or creation of objects are all feasible.
This is the level of sophistication of Space Opera like Star Trek and Star Wars, though few such genres take the more fantastic implications of the technology to heart.
Magical
Magic isn't a technology unless we really take Clarke's Law to heart; Sufficiently advanced technology is indistinguishable from magic, but it works well as a category of items.
Magic items can do anything, limited only by the imagination of the user and the conventions of the game. As such, magic fits well at the apex of the tech list. But most worlds with magic also have regular technology, and at a much lower level. The trick when designing magic items is to give them the proper flare, make them fit the game and to have at least some sense of wonder.
Almost all magical gear costs an Items schtick to acquire - both because it is rare and expensive, and because you must invest some of your life force into them in order to power the magic.