ScrollRect.horizontalScrollbar

Description

Optional Scrollbar object linked to the horizontal scrolling of the ScrollRect.

using UnityEngine;
using System.Collections;
using UnityEngine.UI;  // Required when Using UI elements.

public class ExampleClass : MonoBehaviour
{
    public ScrollRect myScrollRect;
    public Scrollbar newScrollBar;

    public void Start()
    {
        // Assigns a scroll bar element to the ScrollRect, allowing you to scroll in the horizontal axis.
        myScrollRect.horizontalScrollbar = newScrollBar;
    }
}