Tradable Self-Made Mann Co. Supply Crate Key
Self-Made supply crate or case keys, as well as applicable bundle packs, are awarded to players whose items are featured within them. They are usually non-tradable, but glitched variants exist in tradable form.
There are around 28 known instances of tradable Self-Made keys.
Source
Self-Made Specialized Killstreak Mann Co. Supply Crate Key
Team Fortress 2 Level 50 Tool
★ Unusual Effect: Community Sparkle
Sheen: Mean Green
Killstreaks Active
I made this!
Used to open locked supply crates.
This is a limited use item. Uses: 1