Classic knuckle 3D model is available on CGTrader for $16. Original author: HQ3DMOD. Specs: 5944 polys, 5936 verts.
OBJ (OBJ, filesize: 198 KB), TEXTURES (Textures, filesize: 7.31 KB), FBX (Autodesk FBX, filesize: 1.17 MB), MAX (Autodesk 3ds Max, filesize: 373 KB), GLTF (glTF, filesize: 936 KB)