The coxandcox bamboo stool-ladder consists of many elements, everything is assembled into one object and multimaterial is assigned. All materials were renamed and simplified as much as possible, I converted the materials of Corona Render and did not check in the scene for rendering.
Dimensions (HxWxD): 535 x 405 x 375/480 mm
There are no materials in the OBJ file, only geometry.
Who works in the V-Ray version lower than 3.1, be careful, in the materials in the BRDF section there is Microfaset GTR (GGX), if your version is older than 3.1, then the BRDF field will be empty. Choose Blinn, Phong or Ward - which is preferable for you. https://www.coxandcox.co.uk/aalto-step-stool