1. Mobius ring is formed by winding a paper tape and connecting it end to end. It has only one face and one boundary. This structure is widely used in mathematics and physics, such as making data structures in computer science and simulating quantum Hall effect in physics.

2. A plain ring refers to a bracelet without extra decoration or special production, and usually consists of a simple metal wire or chain. The design of plain ring is simple and generous, suitable for daily wear.