The stepper gets hot. Can't turn down the driver any lower without it skipping. So it needs a fan.
The fan mounts coaxially to the stepper. Not that it needs to, but it was a design goal. I was going to solvent weld the standoffs, but realized it works well as separate pieces. The velocity stack at the inlet. . . well, why not?
The mount uses M3 x 35 mm bolts which replace the original extruder mounting bolts. I have a 40 mm x 10 mm motor attached with 18 mm bolts. 16 mm if you don't use the inlet. You'll need a ball-ended hex driver if using the inlet. I used a tap to cut threads into the mount. It holds well.