First of all, no you don’t have to use fresh key limes. You can still make a tasty lime pie with any variety of lime. However, if you can get key limes, I recommend you use those! Key limes, also known as West Indies limes, West Indian limes or Mexican limes, are smooth, round and small. They have a more intense flavour than the regular Persian limes grocery stores carries year-round. If you want to make a key lime pie from scratch but you can only get regular limes, it will still be delicious!