Standard door knob Free (Polygon mesh 3D model) is available on CGTrader for free. Original author: Skysunlimitedesign. Specs: 116424 polys, 156702 verts.
STL (Stereolithography, filesize: 5.55 MB), OBJ (OBJ, filesize: 10.4 MB), BLEND (Blender, filesize: 14.3 MB), DAE (Collada, filesize: 29.2 MB), STP (STEP, filesize: 4.04 MB), ABC (Alembic, filesize: 8.23 MB)