Straight and True. The nut turns the screw under gravity. Threaded mounting holes make installation easier. Edited the Marlin Configuration.h file to set the Z axis "DEFAULT_AXIS_STEPS_PER_UNIT" to 400 and it works fine with my stepper controller (yours may be different). Four stars instead of five because the nut is a bit sloppy, but no big problem so far. A compression spring will most likely fix this.
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