Snapping game object to another game object in Unity 3D during runtime

Question

At this moment, I drag my game-object across the screen; however, I'm having a hard time figuring out how to have my game-object snap to pre-existing game-object in my scene. How do I have my game-object snapped to another object during run time once it is instantiated?

public class DragObject : MonoBehaviour

{ 
    private Vector3 mOffset;
    private float mZCoord;

    void OnMouseDown()

    {
        mZCoord = Camera.main.WorldToScreenPoint(
        gameObject.transform.position).z;
        mOffset = gameObject.transform.position - GetMouseAsWorldPoint();
    }

    private Vector3 GetMouseAsWorldPoint()

    {
        Vector3 mousePoint = Input.mousePosition;
        mousePoint.z = mZCoord;
        return Camera.main.ScreenToWorldPoint(mousePoint);
    }

    void OnMouseDrag()

    {
        transform.position = GetMouseAsWorldPoint() + mOffset;
    }

}

LoadAssets class:

public class LoadAssets : MonoBehaviour
{

    bool isCreated = false;
    bool isCreatedDrillbit = false;

    public void LoadBOP()

    {
        if (!isCreated)

        {
            GameObject instance = Instantiate(Resources.Load("BOP", typeof(GameObject))) as GameObject;
            isCreated = true;
        }

    }

    public void LoadDrillBit()

    {
        if (!isCreatedDrillbit)

        {
            GameObject instance = Instantiate(Resources.Load("Drillbit", typeof(GameObject))) as GameObject;
            isCreatedDrillbit = true;
        }

    }

}

Answer 1

Write a script that checks the position of some other object, and if it's close enough, make it a child of itself and set its local position and rotation to be the default. Also, disable the dragging script:

public class SnapToMe : MonoBehaviour
{

    public GameObject target = null;
    public float snapDistance = 1f; 

    void FixedUpdate() 
    {
        if (target==null) return;

        if ( Vector3.Distance(transform.position, target.transform.position) <= snapDistance) )  
        {
            target.transform.parent = transform;
            target.transform.localRotation = Quaternion.identity;
            target.transform.localPosition = Vector3.zero;

            target.GetComponent<DragObject>().enabled = false;
        }
    }
}

On the object you'd like to do the snapping, add a child object where the snapping should occur, and attach the snapping script to it:

Bottle
└── Bottle snap point
    └── SnapToMe

Then when you create the cap, tell the snap point about it:

Gameobject newCap = Instantiate(...);
Gameobject bottleSnapPoint = GameObject.Find(
        "Bottle snap point"); // or some other way to get a reference to the snap point

SnapToMe snapper = bottleSnapPoint.GetComponent<SnapToMe>();
snapper.target = newCap;
snapper.snapDistance = 2f; //whatever is appropriate