How to remove space between cells in UICollectionView?

How to remove space between two cells in UiCollectionView? Min spacing is not working.

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    if (collectionView.tag==101)
    {
        return CGSizeMake((_collView.frame.size.width),(_collView.frame.size.height));

    }
    else
    {
       return CGSizeMake((_collView2.frame.size.width/3)-20,300);
    }
}

But this is not working.