This two piece part replaces and adds to the acrylic stock cover on the Creality CR-10's Z-axis lead screw; It lets you manually control the hot end up and down (when steppers are disabled), which I have found to be VERY handy at times. For example when you're loading filament, stopping a failing print or first layer, you can easily lift the hot end by hand to give you more working space and a better view of the piece.
I have now also added a bigger version. This way it takes less spinning to manually up and down the hotend. Easily fluently movable with just one finger. (09-15-2018)
FIX (as of 02-10-2018)
Thanks to Thingiverse user wonkoderverstaendige I found out there was a tiny (but real) problem with the file of the big version. Basically the knob floated 0.002mm above the stem, which only caused a problem when sliced in particular way, but it had definitely a weak spot. So if yours snapped, this is probably why. You should have no problems with the fixed file anymore. Sorry for the inconvenience if it got you frustrated!
A simple quick and dirty video by me of how the knob works:
Chuck Hellebuyck on how to install the knob (and other useful CR-10 mods) on Filament Friday:
(3 minnutes and 23 seconds in)