replacement doorknob for shower

When the chrome layer starts to peel off, this is the thing you want to print ;)
Knob is designed for an M6 bolt&nut.
Print with the hole down on the bed and pause just before the hexagon cut out changes back to a circle. Check this in your slicer and note the height or the layer number.
If you use a bolt, you will need to print the knob at a height of bolt length -15mm or -10mm depending on the STL you use. Add a couple of mm for safety.
I use Simplify 3D to slice and one can put an object at some height above the bed and then generate support. Modify support as needed and don't forget to remove all support under the hole where the bolt has to be inserted!
I included 2 versions (see cross sections above) for different bolt lengths. Holes are 25mm deep. Bolt starts in the 15-5-5 version at 15mm, in the 10-5-10 version at 10mm.

You could also use 2 versions with a nut and use a piece of (stainless) threaded rod