how to get the most right point or left point atc of object as visual on the screen in 3d project?

i want to check if the position x of the mouse is bigger or smaller from maximum right point of object on the screen so i check the bounds.max.x of the particular object(mathf.max of x bounds after converting him to screen position)and compare him to mouse x position but the problem is in 3d world its 3 dimention and the very right point on the visual screen its not always actualy bounds max x position of object (i addaed 2 pictures for batter understending me what is mathf.max of x bounds of object in different angels) my quation is how can i get for exemple the most right point or up point atc of object on the screen