# Is it possible to do a radius constraint in Blender?

Is it possible to do a radius constraint in Blender? For example, consider 2 cubes, 1 unit apart, as the following;

[]--1 unit--[]


If we move the box on the right up or down, it will retain same distance as the following;

    []
/
1 unit
/
[]


This is not for Blender Game Engine, I simply want to set up constraints, but can't see of how to get it done in Blender.