Summary

The stock bracket that holds the 40mm fan inside the case (which is cools the stepper motor drivers) is a pretty rubbish piece of acrylic.

So I made one up that will allow you to use either a 4010 or a 4020 fan instead.

You'll need 2x M3 nuts and 2x M3 bolts of the appropriate length (15mm for 4010 fan or 25mm for a 4020 fan) to hold the fan in place. The existing bolts for the base can be reused.