> For the complete documentation index, see [llms.txt](https://gum-ball.gitbook.io/gumball-protocol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gum-ball.gitbook.io/gumball-protocol/overview.md). # Collection Keys When an gNFT collection is launched on GumBall Protocol, a corresponding amount of ERC20 tokens are also created for that collection. These **collection keys** are specific to each gNFT collection and represent a fungible version of 1 NFT. A user may mint a gNFT on GumBall, then swap to the collection key of the gNFT. Collection keys are what is actually bought from the bonding curve and subsequently used to mint a gNFT from the GumBall Machine contract. This was done manually in GumBall V1, with V2 introducing a zapper for users to directly deposit $WETH to mint an NFT. Collection keys help bridge the gap between liquidity in a collection’s bonding curve and the NFT itself, while allowing for deeper composability within DeFi. Both collection keys as well as gNFTs function similarly on GumBall in terms of staking and borrowing. "GBT" is used to represent collection tokens in these documents for brevity.