Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:3331622.

This is an S Hook, designed to hang on Grab Bars / Hand Rails up to 35mm diameter. The large internal diameter is 35mm, the smaller diameter is 20mm and the width is 10mm.

This is designed to suit the grab bars for elderly or disabled people which are typically fitted in shower cubicles and bathrooms. It should suit rails from 32mm - 35mm diameter, although it could easily be scaled to fit other types of rails.