Hmm, didn’t know that. I too had gotten tired of the Z nut slipping free on me so I printed in ABS, then superglued the nut in place (ABS chemically bonds with superglue in a way PLA doesn’t). Since then I’ve switched to a TR8*8 instead of the all thread ($10-15 on Amazon for the screw and nut), and upped my Z axis speed significantly. I think it’s a worthy upgrade worth considering vicious1. The TR8*8 came out of the bag so frictionless that if I started it turning – the nut would turn on it’s own just from gravity until it fell off. (once it’s mounted of course the tool’s weight pushes down enough that it no longer moves on it’s own) I’ve even been able to up my Z axis speed to 40mm/s. (Worked at 50mm/s too, but I didn’t like the sound of the stepper motor – so for safety I took it back down to 40mm/s). That’s travel speed – not plunge speed of course.