This is a nylon top mount bi-fold door pivot. Used by a variety of manufacturers, the solid nylon base is 3/8 inch nylon pin inserts into the top pivot bracket above creating a pivot point for the bi-fold door. See Prime-Line part N 6823 as a possible pivot bracket.
This pivot and guide is constructed from solid nylon. It features a 3/8 in. diameter base and a top mount design. This part is used by many wardrobe door manufacturers.