Mann Co. Supply Crates are tool items obtainable through the item drop system. They are shown as open-style wooden shipping crates, wrapped in chains held with a large padlock. Mann Co. Supply Crates can be opened with the use of a Mann Co. Supply Crate Key. Anything unboxed using an untradable key will become tradable on the date the key is supposed to become tradable.
When a crate is opened, a five second timer ticks down, alongside a sound effect of chains jangling and wood creaking. Once opened to the tune of a cheering crowd, identical to when an achievement is unlocked, the player will receive one among a set of items which are listed in the crate's description and are dependent on its series. This item is announced to the server in a similar format to regular dropped items. After which, both the crate and the key are removed from the player's inventory and replaced with the uncrated item.
While Mann Co. Supply Crates are obtained through the item drop system, they do not add to the total cap of items a player can obtain each week. Furthermore, crate drops are completely independent from weapon or hat drop rates.Scorched Crates and the Summer 2013 Coolers were exceptions as they were not dropped. Scorched Crates could have been the only item inside a Pile of Ash, and the Coolers could only be obtained through Summer Claim Checks.
Though the notion and concept of a crate suggests that the contents should be predetermined, Robin Walker has confirmed the mechanics are such that item drop is determined at the point of opening the crate; moreover, items are not mapped to crates and thus there is no distinction to be made between two crates of identical series.
Mann Co. Supply Crate Series #1 and #2 no longer drop in game. (People with Series #1 and #2 crates still had the attributes set to #1 and #2, but they took on the schema ID of Series #3 and #4 crates, respectively.)
Removed Crate #60, Crate #75, Crate #76 and Crate #77 from the drop list.
An unused 'Special Crate' backpack icon exists in the VPK.
Attempting to open a crate whilst disconnecting from a server will result in the timer being set to 1,000 seconds.
Although Valve modeled the padlocked chain for the icon, the padlocked box can't be found in the game files; its textures, however, can be found. The crate itself uses a model that appears to be the same as models/props_hydro/barrel_crate_half.mdl.
Prior to the Two Cities Update, crates with expiration dates (such as Festive Winter Crates and the Refreshing Summer Cooler Crate) were not actually removed from player backpacks until Team Fortress 2 was started up.
The unused 'Special Crate' backpack icon
In-game crate expiry alert
In-game announcement that the Summer Appetizer Crate has begun dropping