Where is Duchamp's "readymade" Hat Rack, 1916?
There seems to be many, not just one Hat Rack and they are weirdly shaped...see for yourself

This is an actual hat rack found in the 1910's era. This particular hat rack model by Thonet is the closest design to Duchampís Hat rack, 1916, as it is depicted in his two studio photographs. However, as typical of real mass-produced and functional designs, the hat rack is symmetrical and regular in shape.

Interactive Hat Rack Software Instructions:
       Created by Rhonda Roland Shearer, Vitorio Marchi, Robert Slawinski

Please test out the Interactive Hat Rack Software. To select a hat rack click on one of the 5 icons shown on the left. Hold the left side of the mouse down. Making sure the cursor's hand icon switches on (while the arrow is moving) roll the mouse on the hat rack's round base and "pull" the 3D model off its fixed position in the 2D representation. While you explore these 5 models, always keep the left side of the mouse down, beginning with the hat rack's base, and roll the mouse in various directions, and compare the 3D shape of the hat rack to the 5 enlarged 2D images. (Click where it says "enlarge" next to 5 icons). Rotate each of the 5 hatrack 3D models in all x, y and z directions that are possible in 3D space (north, south, east, west, up and down). Try to visualize the 2D representation that you choose as a 2D slice (cut), or only one fixed perspective view of the 3D hat rack form. Also, practice placing the 3D models back into the best possible position matching the 2D depiction you have chosen. Click "reset" button to go back to start position.