I see a lot of people adding this to collections called "Things to Make" or similar. If it's not clear enough from the image, this isn't an exact replica of the original part. The threads are missing, because this is just meant as a place-holder to be used, e.g. in a CAD design, to show how it would fit or how it should be modified. It would be completely useless as an actual part, except perhaps as a lost-PLA master for a casting which would then be threaded manually.
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This is a mock-up of the brass nut included with the 4-start acme threaded rods sold by a number of Ebay sellers. The dimensions were taken from a mechanical drawing posted on one of those listings.
I've included the original Sketchup (ver. 8) model and an STL. The .SKP is in meters, for reasons known to most SU users, but the STL is in mm.
UPDATE: There is also an anti-backlash version of this nut.