This is an adjustable stainless steel cake ring. 
It is used for making mousse cakes, tiramisu, and other desserts. 
The diameter is adjustable, typically from 6 to 12 inches (16 to 30 cm). 
It often features measurement scales on the side for easy size adjustment. 
It is reusable, durable, and safe for use in ovens, refrigerators, and dishwasher