Microgate rings are made from unobtanium, through a difficult forging process with some magical action required. (This would be a good spot to use another of the styles submitted, if there is one that is appropriate.)
Once a pair of gaterings is forged, pressing a trigger connected to one of them will cause the paired rings to become physically connected, so that material and sound and light may pass through them. Some uses of gaterings include long distance communication and "wands," where one ring in a pair is kept in a vat of pressurized fluid, and pressing the trigger makes the fluid stream out of the other ring.
After long use, as the unobtanium is used up, the rings shrink to the point of unusability, and may break.
The largest microgates are just large enough to pass a newborn baby through, but these are extremely rare. Because the supply of unobtanium is so low, and because larger rings are less stable, ring forgers prefer to use their supplies to create a number of small gatering pairs.
Tradition
A couple thousand years ago, unobtanium was relatively common, and the histories from that time are full of references to microgates. Since that time, most of the available supplies have been used up, and most people believe that microgates never existed, or that they were a lost application of another style of magic. The tradition of gatering forging has died out completely, although it lingered for a long time in a few remote pockets of civilization, and the process is described in detail in an ancient manuscript that is still extant. Quite recently, new supplies of unobtanium in the colony lands were discovered, and a new golden age of microgating is poised to begin. A few practitioners of other styles of magic may have learned a little bit about microgates, and may look down upon their users as counterfeits who fake the effects of real magic with tawdry tricks.
Many microgate rings ended up in the collections of monarchs and extremely wealthy nobles, most of whom don't have the slightest clue what they are sitting on. (The ones who passed down the knowledge from generation to generation tended to end up with a prolifigate son or two who used them all up. Living microgate using traditions tend to be those that enforce very sparing use of the rings, without quitting their use entirely and then forgetting how they are used. Some religious orders have a few gatering pairs, as do some traditional "elite palace guard" type military units, and some secret societies. Scattered individuals have a single ring pair.
School
The Custodians of the Relics of [Folk Hero]
The CRFH is a secret society headquartered in [Large Capital City]. Lower level members of the CRFH are given a box which they are told contains a relic of [Folk Hero], but which is really empty. They are told they must never open it, on pain of banishment from the society. After many years, (the length of time depends on the number of rings available and on the quality of an individual's service to the society) they learn that the box was just a test, and if they passed, they are inducted into a deeper circle that keeps the secret of the gaterings, of which the society has acquired a fair number.
Members in this circle are allowed to use gaterings only for self defense, or to communicate in dire emergencies. The highest level of leaders has a little more leeway in how they may use gaterings, but they still tend to be conservative in their use. Some of them have a keen interest in advances in chemistry, as a source of materials for wands to emit.
The dirty secret of the CRFH is that most of their rings are stolen. They believe that they alone are the proper custodians of the gaterings, and that they must liberate them from anyone who might abuse them. Some of them have become very good thieves, although they have pleged never to use that particular talent except in the service of the society.