We know Apple has a love affair with thin. The iPhone 5 is the thinnest iPhone ever. The MacBook Air could very well be used to slice bread. And the svelte MacBook Pro with Retina Display shows even premium notebook offerings can stand to shed a few pounds.

Still, when Apple unveiled the new 21.5- and 27-inch iMacs at its media event last week, it was shocking just how much thinner Apple had managed to make them. They seemed almost surgically precise, the result not just of remarkably slim displays but also an advanced welding technology borrowed from the aerospace industry.

Apple cut the volume of the new iMac by 40 percent. The LCD display is 45 percent thinner than that of the previous generation's, which equates to 5 mm shaved off the total thickness. “The iMac display is really not getting the attention it deserves,” IHS analyst Vinita Jakhanwal told Wired. OLED displays are known for being lighter and thinner than their LCD counterparts, but Apple seems to have bucked that trend. “If it’s anywhere close to OLED display thickness, that’s something really cool.”

LG, for example, introduced a 55-inch OLED TV at CES last year that was 4 mm thick, and a few years before that, Sony demoed an 11-inch OLED TV that was only 3 mm thick. Since the edge of the iMac is only 5 mm thick, it's safe to assume that the LCD display is down in OLED territory.

NPD DisplaySearch analyst Paul Semenza explained via e-mail how Apple managed to make the iMac display so thin, and the benefits of that process: "Apple is using optical bonding (lamination) of the [LCD] panel to a sheet of strengthened cover glass. This eliminates the air gap between the panel and the glass, which reduces overall thickness, and the optical bonding eliminates the reflections between the inside of the cover glass and the outside of the panel, which improves image quality."

This may sound similar to the process used to make the display in the iPhone 5, but it's actually less complicated. The iPhone's display is higher resolution and has integrated touch sensing, which makes it more challenging to produce. Jakhanwal says that Corning and other glass companies have been working to reduce the thickness of that cover glass, too. In recent years, it's come down from over 0.7 mm to 0.3 mm.

Apple took full advantage of the thinner displays by creating an ultra-thin body to go along with them. The new iMacs are just 5 mm thick for the entirety of the desktop’s perimeter. To maintain that along seams where the front and back pieces meet, Apple used a process called friction stir welding (FSW) – a method normally reserved for things like airplane wings and rocket booster tanks, areas that need a seamless, fail-safe connection. It was even used on parts in the Space Shuttle.

FSW is a solid-state process, meaning the metal isn't melted. In simple terms, it works by using a rotating tool pressed against the surface of two overlapping plates. The tool has a small protrusion that fits into the crack between the plates and is pressed down along the length of the joint. This creates frictional heat that softens the two surfaces, which are then pressed together under high pressure to create a bond.

FSW was invented by Wayne Thomas at TWI Ltd, a U.K.-based independent research and technology company. Because this is a patented process, Apple is licensing the technology for its iMacs. A TWI representative said that the specific details of that license are confidential, but it looks like Apple is the first consumer electronics company to employ the technology. Of course, if the rest of the industry follows Apple's lead – as it is wont to do – TWI could be getting a lot more customers.