Dials

Dials are strange, mysterious devices in One Piece. They look like shells, but have the ability to store energy. They come from Sky Islands such as Skypiea and in some cases, may be only found on a single one, or go extinct. How exactly they are created or how one can go extinct is unknown. All that is known is that they are gathered from the sea, very close to shore. It has been suggested that they may grow somehow.

Dials In General
There are many types of dials, some native to specific Sky Islands. Most seem to be common, though. Dials store energy itself, usually by that particular type of energy being directed at tiny holes on one side of the Dial. The energy is then stored for later use. Dials do not seem to lose an amount of energy due to no use, like a battery might if attached to a device.

On the other hand, dials do not appear to use all their energy in one blast, although it has been implied they do, or should. It could be the Dial can regenerate so much, or generates more energy for a backup from the loaded amount. There is a small chance, however, that for story progression and plot reasons, they are allowed to use all their energy more than once. But this is unlikely. Some Dials obviously let the energy out in different amounts, while some it would make more sense for all the energy to be used.

Axe Dial
The Axe Dial (斬撃貝(アックスダイアル), akkusu daiaru, "slice attack shell") is not found in Skypiea and is used for whatever the Impact Dial isn't used for, weapon wise. The axe dial delivers a thin blast of air capable of slicing through a man and his shield in one blow. The 50 Goat-Like Enforcers each have one, and their main leader, Yama, has a vest of them. Like the Impact Dial, its main use is mainly in Sky Warfare, but in some situations may be appropriate for other uses. So far, there has been no mention of a more powerful version of the Axe Dial. There is a chance, though, that the Axe Dial is the more powerful version of another, yet unknown, Dial.

Ball Dial
This dial releases a puff of cloud that forms into a ball shape upon being released that can be sat or stood on.

Breath Dial
The Breath Dial (風貝(ブレスダイアル), buresu daiaru, "wind shell") is capable of storing air-current energy. Many common uses are in wavers where they are used to propel the waver through the water. Some other uses are catching strong winds, to be used later on a ship if there are no wind-currents to use for sailing. Like many dials, there are other creative uses. Breath Dials, unlike Jet Dials, carry smells and aromas as well. They are handy for storing gases of some sort, such as poisons. Usually, though, it is used to let off a strong stink, used to force enemies into covering their noses.

Flame Dial
A dial that absorbs and releases flames, not to be confused with Heat Dials. Shura's giant bird Fuza has one in its mouth that enables him to breathe fire. Burn Blades also contain them.

Flash Dials
Flash Dials (閃光(フラッシュダイアル), furasshu daiaru, "flash shell") is one of the two types of Dials that store, and then produce light. The Flash Dial lets out extremely bright, probably uncontrolled amounts of light for a very brief period, effectively causing temporary blindness if looked into by somebody. Usopp uses one in his fight against Luffy.

Flavor Dial
This dial can store smells and aromas, along with other types of gas such as explosive ones.

Heat Dial
The Heat Dial (熱貝(ヒートダイアル), hīto daiaru, "heat shell") stores Flame Energy. It is commonly used to make ovens and other such heating devices for citizens of a Sky Island. It appears to be able to let out heat in different amounts, unlike most Dials. The only heat dial seen in sky warfare belongs to the Priest Shura, who uses one with his lance to make it red-hot.

Impact Dial
The Impact Dials (衝撃貝(インパクトダイアル), inpakuto daiaru, "impact shell") may be hit by anything blunt, or that does not slice (although it was shown absorbing axe and sword strikes in filler), and will take in that energy. Once the apex of the Dial is pressed, the energy stored in the dial from the weapon is released, usually targeting the inside of the body, usually not leaving a trace on the outside. This blunt force is even enough to wound Luffy, who is usually only susceptible to bladed weapons. In chapter 466 it was revealed that the Impact Dial can also absorb the impact of explosions.

The Impact dial, while not as dangerous as the Reject, still can hurt the user after a large amount of energy is released, usually Usopp as he uses them most often, but also Nami in her fight against Kotori. The Impact Dial, like most Dials, is activated by pressing the apex of the shell, on the back side of the Dial. This is the side opposite of the holes that let the energy out. It's unknown the limit of impact it can absorb, but so far it was able to absorb all the impact it was given to.

Jet Dial
The Jet Dial (噴風貝(ジェットダイアル), jetto daiaru, "wind jet shell") is a more powerful version of the Breath Dial, which blows out a burst of air great speed. It is now extinct, but was once common in Skypiea. They were once used in wavers when they were common, but were replaced by Breath Dials when they became extinct. How they became extinct is unknown, but some are still in existence. The term extinct seems to refer to them being no longer findable on the Sky Island or they seems to have stopped being created. If the theory that they grow is true, then they may just stop growing, due to a few possible reasons. They can also be used in battle-Enel's warship has a backup propulsion system powered by 200 Jet Dials and the priest Gedatsu wears two on his arms to increase the speed of his punches. This suggests that the Jet Dials were native from Bilka, Enel's and his priests' homeland, and after this land was destroyed all of the Jet Dials became extinct.

Lamp Dial
The Lamp Dial (灯貝(ランプダイアル), ranpu daiaru, "lamp shell") is similar to the Flash Dial and stores light. However, its most common use is the home not the battlefield unlike the Flash Dial.

Milky Dial
The Milky Dial (雲貝(ミルキーダイアル), mirukī daiaru, "cloud shell") can store energy of some sort, what exactly is unknown, and create or release clouds. Often the clouds are created then a device that can float on a cloud will be used, for many different reasons. Reasons may include, but are not limited to, reaching high places, making a path, crossing a large gap between land, or another solid place, and sometimes to launch an attack on an enemy. Many of these can be used for both every-day reasons, such as maybe getting a pet out of a high place he or she is stuck in, or in military circumstances, like attacking an enemy in a high place, quickly. The Warriors of Shandra have a type of in-line skates, with Milky Dials in them. The Milky Dial allows them to skate smoothly across the cloud, but leaves a cloud-trail behind the user.

Reject Dial
The Reject Dial (排除貝(リジェクトダイアル), rijekuto daiaru, "rejection shell") is a much stronger version of the Impact Dial. It is extremely rare to find, and also extremely dangerous to the user, as well as the victim. The Reject Dial takes in energy just like the Impact Dial, except it releases 10 times as much energy. There is always a risk to the user, of blowing his body to bits as well as the victim's, especially with repeated use.

Tone Dial
A dial that is able to record and replay sounds spoken into it. Since it has no use in battle it's rarely used.

Vision Dial
The Vision Dial (映像貝(ビジョンダイアル), bijon daiaru, "image shell") is used for capturing images and showing them. It is currently unknown if it is capable of video capturing, and a picture of it displaying has never been created. Exactly how it displays is also unknown because of this. The Vision Dial is comparable to a modern-day Camera. It likely would not have many uses in Sky Warfare apart from scouting. Like the other Dials, it probably makes Sky Island life more similar to our modern-day society.

Water Dial
Though not seen, it is presumably used to absorb and release water.

Sky Warfare
On Sky Islands, battles are fought much different than down in the Blue Sea. Oftentimes weapons are upgrade, or even combined with Dials. This allows for incredibly powerful weapons. Many times Dials are used in creative ways. Milky Dials, for example, are commonly used to rush towards an enemy, if the user has some sort of device to help traverse the path created by the Dial. Heat Dials are usually found inside weapons. Breath Dials are commonly used to create a stink-cloud or produce a poisonous gas. Impact Dials, and to some extent, Axe Dials, are commonly used in Sky Warfare, likely 50% or more of Dials used in Sky Warfare or another type of Combat are Impact Dials and Axe Dials, Impact Dials being much more common outside of standard-issue Dials. Many times, tactics revolve around Dials, and fighting an opponent with Dials while you have none yourself will usually put you at a huge disadvantage. An opponent using a Milky Dial, along with a type of transportation across the Milky Dial's path, and a Light or Heat Dial in their weapon, will have no problem moving to a more convenient location, and then having a leg-up on firepower and/or aim. A person may be blinded by a Light Dial, while the user uses the Milky Dial to move to a better location, and then uses a Heat Dial to shoot an extremely powerful shot at the blinded opponent.

Impact Dials, as well as Reject Dials and Axe Dials, are generally hidden under Bandages or a Glove during Sky Warfare. Sometimes even Breath Dials, filled with noxious or stinky smells, will be hidden as well. This allows for sneaky attacks, because the opponent likely will not know what kind of Dial would be used, or if there even is one, until they are hit by it. Even then some tricks may prevent the victims from knowing exactly where the Dial is. Many warriors in a Sky Island will be almost entirely immune to an Impact Dial, which would normally kill, or badly injure a normal person, or even a soldier. However, not many can take a hit form a Reject Dial and come out alive. The Reject Dial is generally frowned upon by allies of a user, because it may very well annihilate the user as well as the victim, even when perhaps the extra Energy was not needed, and an Impact Dial may have done almost as good of a job. This makes the Impact Dial much more popular. The Reject Dial even almost killed Enel once, however, he survived by reviving himself, using his Devil Fruit powers,when he pulsed his heart until it started itself again.

Trivia

 * Usopp traded many of his items that were rare or never-before-seen in Skypeia for Dials; things such as rubber bands. Rubber is a mystery to people on most, if not all Sky Islands since it does not exist in the White Sea.