This drain kit does not include a strainer as the top grate acts as the strainer. It does include a nylon threaded adapter for mating to standard 2" drain bases which are typically already installed by your plumber or contractor.

So, this is the only thing I have to buy? The basket is optional, but the gasket to attach to the drain isn't. Are there any other required parts?

Correct - basket strainer is optional. If your drain base is installed then you will have everything you need in our kit.