In Israel, a five-shekel coin is used to free supermarket carts,
The diameter of such a coin is 24 millimeters and its thickness is 2.4 millimeters, I have no idea what is the case in other countries, but I assume that in other countries there is a coin of the same size
The ring is a minimalist way to make sure we always have how to take a cart in the supermarket its printing time is short, convenient to store it in a wallet and convenient to put it on the finger if it is not convenient to open the wallet straight when returning the supermarket cart
The diameter of the inner ring is 17 millimeters I have attached a SolidWorks file so you can fit for your finger and your coin
The author hasn't provided the model origin yet.