A 3D scale[conjectural title] is an interactable object found in Kirby: Triple Deluxe. It consists of two platforms attached to a scale, which is draped to place each platform, often in a different plane. Characters, enemies or items resting on one platform will cause that one to sink and the other to rise until a certain threshold is reached, where the movement will stop.
Scales can be arranged in several fashions, including in unbalanced ways that favor one platform over the other. Kirby will often have to make use of these objects to create stepping stones to carry other items, or to open up a way down below one of the platforms. The platforms themselves are semi-thin, meaning they can be jumped through from below, but not from above.
For functional purposes, Kirby (or King Dedede), standard enemies, and keys are all treated as having the same weight. As such, if Kirby carries a key while standing on a scale, he will weigh twice as much as he normally does.