First invented in 1962 by Mr. Ermal Fraze, the ringpull- or pop tab, or pop top- was first marketed by the Pittsburgh Brewing Company. Evolved by Fraze from the zip-top, it is now the most common design for a canned-drinks lid, and is used all over the world.
To see why the ringpull was invented, we must look at the entire design of the can, old and new. Originally, cans of drink were not made from aluminium, but from atype of tin-coated steel called tinplate. This made them expensive, heavy, and rather hard to open: they had to use a church-key system- as found in the modern day on some tins of corned beef- as most other designs were unable to help break the tough steel. (There was also a design called the "cone top", which looked a lot like a bottle, and was often opened with a can-opener or, with some designs, a bottle opener.)
Eventually, in 1958, Kaiser Aluminium started marketing the light-weight aluminium cans to others.
This in itself meant other designs rather than the common church-key could be used; but the general public were fairly happy with the design, piercing with the church-key and pouring into glasses. It only really became an issue if such a church-key was not available- in these cases, cans had to be bludgeoned open, normally rather messily.
Thankfully, one person caught without a church-key was Mr. Ermal Fraze, owner of the Dayton Reliable Tool and Manufacturing Company. Caught without this vital piece of equipment at a picnic full of beer, he and his family were relegated using a car bumper to open the cans. This resulted in lots of beer all over the car, grass, and hands, and little left in the cans. This, understandably, wrankled Ernie to no end.
One night, while unable to sleep, Fraze thought about the problem he had encountered at the picnic. In a stroke of inspiration, he realized a way to fit a form of small key to the lid with a tiny lever, and a way to make the lid thin enough to remove but thick enough not to explode under intErmal pressure. In 1963, he patented the device, called the zip-lid.
The design itself is masterful, and is stll used today.
The ringpull is made from a thin sheet of aluminium, cut into appropriate shape, and then folded to make it thicker and less likely to tear.
The modern ringpull generally follows this design:
The line down here separates
the rest of the can from the "hinge"
| This (O) represents the rivet. The rivet
| is cleverly made from the top of the can itself.
/ _____ __ ]
| /| \ / \ \ Both the }s show where the metal
/ / }--\ | | \ | precedes the hinge, bent at a slight
| |[(O)| | | | | angle, making it harder to tear.
\ \ }--/ | | / |
| \|_____/ \__/ /
A small, round rivet, made from the can itself, holds a the ringpull to the top of the can. On this ringpull, a reinforced ring-part at the opposite end of the rivet allows one to slide one's finger underneath it without the ringpull breaking. As the hinge is riveted on, the ringpull can't come loose when pulled; instead, the area where the hinge and the rest of the ringpull meets bends and becomes a fulcrum, allowing the end furthest the ring to push down into the lid of the drink; the entire ringpull is a force multiplier. The area it presses down on is notched all around except for a small area to one corner, allowing the drink to open up, but for the piece of aluminium the ringpull displaces not to fall into the drink.
Interestingly, while ringpulls today press down a small, notched area that bends into the drink, they originally sat on top of the notched area; the idea was you pressed them down and pulled them back, much like while opening cans of dog food with ringpulls today. This design was soon scrapped as people kept dropping the sharp ringpulls on the earth, cutting people's feet.
Ringpulls have been used for many years for many other things, too. Some charities--such as the Ronald McDonald House- take in the ringpulls for recycling, then give the money earned in this way to their cause. This is because the public believes that ringpull is the most pure part of a can; while the rest of the can is various alloys mixed in with aluminium, the ringpull is almost 100% aluminium. A pound of aluminium is worth about 40 cents; and a ringpull weighs about 1/1200th of a pound.
The truth is, there is nothing special about the Ringpull's purity. Instead, it's the same as the rest of the can-- and worth very, very little. One is much better off giving away the entire can: it is only McDonald's extreme generosity that gives them a reason to take in ringpulls.
Understandably, while Ronald McDonald House does take in ringpulls for a good cause- whether it can actually use them or not- most charities do not. In fact, there have been many rumors about fund-raising projects that involve recycling ringpulls over time, often found in spam e-mail. Also, while some recycling companies pay for ringpulls and cans, others don't: this is because of how little a ringpull is worth.
Companies sometimes paint the hidden, undersides of ringpulls, and leave out the hole in the loop. This can be used to hide serial numbers for competitions; Dr. Pepper, for example, sometimes puts up cans as prizes. Once you've bought the drink and opened it, you can look at the ringpull; if it reads a DRP you win an extra can, and if it reads XXX you win nothing.
Coca-Cola also had red ringpulls for a while, and you could trade in ringpulls online for various goods. However, the number of ringpulls needed was staggering, and it was possibly lethal to consume that much of a single carbonated drink.
A common design of the ringpull is the rounded in the diagram above. However, not all of them are so rounded; while rounded ones tend to be found on soft-drinks, alcoholic beverages tend towards a more stocky, square shape. Also, these square ringpulls can be found on many cans originating outside of the UK and US- in many European countries, the rounded ringpull is unheard of.