A device for holding in position a product to be processed includes a base connectable by magnetic interaction to a work surface of an apparatus for tumbling or polishing and comprising a first portion and a second portion movable along an operating direction mutually towards or away from a first and a second operating position. The device also includes a retaining support connected to the base and configured to hold in a stable position a product to be processed between a first and a second retaining element. Between the first and the second portion of the base an actuation member is interposed, configured to move the same portions between the first operating position and the second operating position. A method for holding in position a product to be processed is also disclosed.