How to make a 3d object act like GUI?

I’m making a first person game where the player is able to see their hands. Because of different screen resolutions, the hands might not show up on all computers the right way if I just made them stay right in front of the camera, so I was thinking about trying to make the hands act like they’re GUI, like in many other first person games, such as Call of Duty. So could I make the hands do that instead of making them a physical game object?

First, the way Unity works is that the amount of world units seen vertically remains fixed across all resolutions. The amount seen horizontally changes as the aspect ratio of the screen changes. The result is that your hands should remain the same across all resolutions. In fact that is just the opposite of what would happen if you used GUI to display the hands. In GUI, things are specified in pixels. So if the density of the resolution goes up, things get smaller…the opposite of what you want for the display of hands.

Referring to the question you ask in your title, many third-party GUI systems use world objects. They use a second, Orthographic camera for the display of objects. This allows for fixed sizes and allows all the object to appear in front of the scene displayed by the main camera.