Every CS2 weapon case has its own set of skins. A case does not select an item from the entire skin catalog. Only the weapon skins assigned to that particular case can appear. From there, the rarity system determines how often different groups of items occur. Other characteristics, including StatTrak, float, and pattern, apply to the individual item.
Every Case Has a Fixed Item Pool
The contents of a case are set in advance. Players can view the skins associated with a case before using it, including the rare special items available from that case. This means an AK-47 skin from one case cannot simply appear in another. The item pool also does not change according to what a player already owns. Using a particular weapon frequently or having several copies of one skin does not add or remove items from the case. The possible results are determined by the contents assigned to that case.
Rarity Tiers Divide the Skins
Skins inside a standard case are separated into rarity tiers. These usually include Mil-Spec, Restricted, Classified, and Covert. Cases also have a rare special item category, which can contain knives or gloves depending on the case. The tiers do not have equal probabilities. Figures commonly used for CS2 case odds put Mil-Spec at about 79.92%, Restricted at 15.98%, Classified at 3.20%, Covert at 0.64%, and a rare special item at about 0.26%. This is why simply counting the number of skins shown in a case does not tell you how likely each one is to appear. A Covert skin belongs to a much less common tier than a Mil-Spec skin.
Rare Special Items
Knives and gloves are handled separately from the regular weapon-skin tiers. A case has a specific selection of rare special items rather than access to every knife and glove. The type depends on the case. Chroma Case, for example, can contain knives as rare special items. The Clutch Case instead has gloves in this category. There can also be several possible models and finishes within the rare special item pool. Reaching this category therefore does not identify the exact item that will appear. It only means the result comes from the special-item selection associated with that case.
StatTrak and Souvenir Skins
Eligible case items can also have StatTrak versions. StatTrak adds a counter that records kills made with the weapon. It does not turn the item into a different finish or move it into another rarity tier. A StatTrak Classified skin, for example, is still the same Classified skin, but it is a different version of that item. Not every cosmetic item supports StatTrak. Weapon skins and knives from eligible cases can have StatTrak versions, while gloves do not. Souvenir skins are distributed through a different system and should not be treated as StatTrak alternatives.
Float and Exterior
After the particular weapon finish is determined, the individual item also has a float value. Float is a numerical value connected to the wear of that specific skin. Exterior names such as Factory New, Minimal Wear, Field-Tested, Well-Worn, and Battle-Scarred correspond to different parts of the float scale. However, not every skin can appear in all five exteriors. Each skin has its own allowed float range. It can vary from 0 to 1. The player has no influence on which skin he will receive, except when purchasing the skin.
Pattern Seed
Individual skins also receive a pattern seed. For many skins, this makes little noticeable difference. On others, it can change where colors and design elements appear on the weapon. Case Hardened finishes are a familiar example because different patterns can produce very different amounts and placements of blue. Pattern does not decide which weapon finish comes from the case. It is a characteristic of the individual item after that finish has been selected. Two skins can therefore share the same name, rarity, and exterior while having visibly different patterns.
Previous Results Do Not Change the Pool
Earlier results do not remove skins from a case or change its fixed contents. Receiving several Mil-Spec skins in a row does not mean a Classified or Covert item has to appear next. The same applies after receiving a rare item. It does not prevent another rare result from appearing later. Each use of the case draws from the same defined item pool and rarity structure. A player's inventory and previous case results therefore do not determine which items remain available for the next one.
Conclusion
What can appear starts with the case itself and its fixed item pool. Rarity determines how commonly different tiers occur, while the items within those tiers provide the possible results. StatTrak, float, exterior, and pattern then distinguish individual versions of those skins.