Mann Co. Supply Crates are randomly rewarded to active Team Fortress 2 players on a timer that resets every week. Each crate contains one random item from the list of possible items in a crate's description. Crates are opened with Mann Co. Supply Crate Keys, which are available from the Mann Co. Store.
Certain items can only be found in crates:
- Strange weapons. These weapons track the number of kills (or other stats, depending on the weapon) achieved with that weapon.
- Strange parts. When used with to a strange weapon, strange parts track additional stats like headshots, critical kills, or projectiles reflected.
- Unusual hats. A hat with a unique particle effect is the "Exceedingly Rare Special Item" referred to in a crate's description. Each crate has just a 1% chance of dropping an unusual hat.
Crates can also contain non-unusual cosmetic items which may also be available from random drops, crafting, and the store.
The list of possible items inside a crate is determined by its series. Valve issues new crate series on an irregular schedule, and only a few different crate series are given to players at any time. Over 60 different crate variations have dropped over the lifespan of Team Fortress 2.