A pentagon? A solid triangular bar?
A lock on a door knob.
An irregular pentagon.
I'm going to take a guess. A 2-D object must have at least three sides (a triangle) A 3-D object must have at least four sides (a triangular pyramid) I'm going to guess that a 4-D object must have at least 5 sides, if the pattern holds...
..... If you have a household runway maybe
Assuming that a space figure means a 3-dimensional object, the answer is a square based pyramid.
20 inches (5x4)
[object Object]
There is no such thing as an object with two sides.
Armchair
Straw
[object Object]