Support for the top of the Z lead screw on an Ender 3 3D printer. This is to prevent accidentally bending the lead screw by rotating it by hand unsupported.

It was originally designed to be used in conjunction with a Z knob by techboner (http://www.thingiverse.com/thing:3179667) fitted to the Z lead screw .
Jan 22, 2019 Update: I have designed a new Z lead screw knob with a finger depression to enable a rapid Z traverse to go with this lead screw support. See:
https://www.thingiverse.com/thing:3373265
I have also designed a matching extruder knob, see:
https://www.thingiverse.com/thing:3373315

It is attached using the spare M4 T slot nuts and M4 socket head cap screws supplied with the printer.
When attaching this to the printer, initially install with the screws very loose. Then raise the gantry to the top before securing the screws. Check that there is no pressure or friction on the lead screw, and that it can rotate freely. Then fit the knob (http://www.thingiverse.com/thing:3179667), and again check that the lead screw and knob rotate freely. don't over tighten the screws as there is a risk of binding the lead screw.

I have added a version with elongated screw slots to provide +/-0.5mm adjustment if you prefer.

Update: I have created an alternative version of this mount that is a press fit into the T slot rather than attached with screws, see: https://www.thingiverse.com/thing:3358957

Update, I have also created an alternate version of the press fit design that is compatible for use with Filboyt's excellent filament guide design, see: https://www.thingiverse.com/thing:3358978

If you like it, make it.
If you make it, post the make.
If you like it and make it, any tips are greatly appreciated.

The difference between the Z lead screw designs are:
This version attaches to the upper rail using screws and T nuts. I designed it this way as I had lights mounted to the upper rail that made it difficult to remove the upper rail to mount the lead screw support. This design allows the lead screw support to be mounted without any disassembly. It also allowed for some small adjustment for position/alignment.

UPDATE: I found that I really did not need the adjustment that the this design provided, so I have redesigned it for a press fit. see: https://www.thingiverse.com/thing:3358957
This allows the lead screw mount to be inserted into the end of the upper rail and has a cleaner appearance, however it requires either removal of the upper rail or removal of the lead screw to install it, but it fits very nicely (I used the tight fit design).

UPDATE: The above two designs are not compatible with the mounting block for the filament guide, so I redesigned the press fit version so that it can work together with the filament guide. See: https://www.thingiverse.com/thing:3358978
This design also requires either the upper rail or lead screw to be removed to install it to the printer, but it works very nicely together with the filament guide. I also used the tight fit version on my printer.