Slip-on flange has a low hub because pipe slips into flange prior to welding. It is welded both inside and out to provide sufficient strength and prevent leakage. Slip-on flanges are all bored slightly wider than the outside diameter of the matching pipe. They are preferred over welding neck flanges by many users due to their lower initial cost, but final installation cost is probably not much less than that of using welding neck flanges because of the additional welding involved.