snaping side by side

Hello Im trying something new. I will put some pictures to make it clear. I have 2 objects and 2 empty game objects as child to the 2 main objects.. http://i.imgur.com/B0gWr1E.jpg What i have done is to say object that i hold when i leave the object it should go to empty game object.. Which it does... Despite that this works my actual intention was to make two object connect from the RED boxes (planes) to each other.. So what i need shortly make them snap each other side by side from the side where the red planes (or empty game objects).. The problem is if i gave the coordinate of the planes half of the parent object goes inside of the other one... Here is my very very simple code...

 void OnMouseDrag() { Vector3 mousePosition = new Vector3(Input.mousePosition.x, Input.mousePosition.y, distance); Vector3 objPosition = Camera.main.ScreenToWorldPoint(mousePosition); offset = mousePosition - this.transform.position; // do nothing at the moment
     transform.position = objPosition;
 }
  void OnMouseUp()
  {
     GameObject game = GameObject.FindGameObjectWithTag("Plane"); 
     this.transform.position = game.gameObject.transform.position;
  }

How can i make my object snap together when i leave my mouse button snap side by side.. ?