Roulette

The Roulette is a feature in the game. It's however only available at rank 10.

Features
The Roulette, when first used, zooms the camera towards a roulette wheel. Depending on the set rarity, the Roulette will bring in parts from the rarities Rare, Unrare, Super Rare, Mega Rare, Hyper Rare, and Ultra Rare (Mythic Rare was in the list before it's removal in 3.8). Many other rarities have been temporarily added, such as during Halloween (Spooky, Scary, and Spoopy) and Christmas (Jolly, Happy, Hyperactive). A rumor spread during the first few updates of the Roulette that the extremely rare Hollow Mountain carrier was in circulation. This was true until 3.8 came along and kicked it out.

Regardless of actual class type, the Roulette's parts when given will always be in a separate class called "Luxury", to differentiate it from most classes. The future update 4.4 will replace Luxury with the normal classes, but there will be a blue star above the tank that reveals it's difference.

Use
The use of the Roulette is for the player to spend coins to spin it and get a random part. However, the amount increases on the set rarity (ex. Ultra Rare; 15k coins, Rare; 500 coins). There have been exceptions however; During the Fallen Barriers update, the price of all rarities decreased/increased to a reasonable 750 (as a warm welcome to new players).

Parts that have been temporarily in the Roulette
There are special tank parts that have been in the Roulette Circulation (as it's often referred to in the files, "Black Market"). For example, during the Dimensional Strike update, 173 (later updated to be 188) new parts could be obtained in the roulette, such as the Physicsbreaker, Newton's Apple and Cutlery could be obtained (all three of these were in Ultra Rare).

During the Particle Acceleration Device update, the P.A.D.M. was the first and so far only part that was a Mythic Rare in circulation. A calculation revealed that there is less than .5% chance of obtaining one, which is why during the event only 17 were ever obtained.

During the Dam Leak update, a chunk of the Hoover (all sixteen were built into the now-obtainable Hoover) could be added. Although it would not be considered a Part, the Hoover chunk could be separately obtained.

The Interstellar Update had the Endurance, a now-obtainable-by-normal-means tank in circulation as an Ultra Rare. Nowadays, it's a Unrare.

Parts that have never been obtained despite being added
The Ika was a squid-shaped tank that due to a glitch, had less than a 1/10,000,000th chance of being obtained. After the update, the otherwise Ultra Rare could be obtained in a very short period of 3 days with a only 90% chance.

Despite being in active service, the Windstorm nearly got wiped out from existance in the Roulette due to a bug involving the obtaining rarity (a 1/45, but the bug set it to 0.00000000000000000000000000000001/10). This was quickly updated.

The Chalkwheel, with a 1/65 chance of obtaining, could have been a 1/2,147,362,918,777,437,921,632,816,457 chance. This would have made it nearly as impossible as the forementioned Windstorm.

Parts that have accidentally went into the Roulette's circulation
Most of the Carriers were added into the Roulette with a chance of 1/15 (the normal version). This was fixed, but carriers like the Stormfront and the Vanguard had increased into the thousands. All were deleted and replaced with the Great Memory, a carrier that had the amount of fighters as a Stormfront.

The Allure was almost put into the Super Rare section despite the original Ultra Rare.

Trivia

 * As of the current version of Tanker (4.4), there have been nearly 3,000 parts added (not counting the 25 Carriers and the Allure.) to the Roulette and it's powerful counterpart, the Core. (The Roulette has nearly 1,900 parts and the Core has 1000. The Supercore, a version in which the Core has 10x the better rarity, has 100 parts)
 * It's currently unknown the exact first part to the Roulette was. Data and other info suggest that the first part was the Knuckler, however it's unclear.
 * The developer has since officially confirmed that the first actual part was the ultra rare Florence.