No Series Number Mann Co. Supply Crate
Mann Co. Supply Crate with no Series number - It is unclear on how these were created. Some say they just found it like that, others say it was created by being in a trade and it timed out sending the glitched item back to the user.
There are about 3 known instances of this item.
Mann Co. Supply Crate
Team Fortress 2 Level 10 Supply Crate
You need a Mann Co. Supply Crate Key to open this.
You can pick one up at the Mann Co. Store.