Capri Tools 8 mm x 9 mm Super-Thin Open End Wrench, Metric (11850-0809)

You want a 9mm wrench with 2mm thick jaws, which are actually pretty hard to find. You might be able to fudge it with a slightly thicker wrench, though. It's honestly pretty annoying that they don't come with a wrench since it's so easy to torque down the shaft with the joystick topper, but impossible to do the same thing in reverse. The only wrench I've found with 2mm jaws is this adjustable one: https://www.amazon.com/dp/B0791X9CXZ EDIT: Actually, I was going off of the dimensions of the SELS-70X shaft. The parallel edges on the Nobi NT shaft are more like 1.5mm in height, so ideally you'd want an even thinner wrench, which I've never found.