I have spent hours on this task and I feel it's high time I asked. My avatar hands go into my chair GameObject.
I added a box collider to the hands of my avatar and unchecked "Is Trigger". I also added a box collider to my chair and its "Is Trigger" is also unchecked. In addition to this, I added a Rigidbody to this GameObject and "collision detection" set to "continuous" hoping that the hands and the game object will collide without going into each other, but they still clip through one another.
I have also tried including Rigidbodies to the hands. Still the same. I have tried many of the solutions under similar problems, but the problem persists.