A Slip-on flange has a low hub because the pipe slips into the 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 larger than the O.D. of the matching pipe. Their lower cost makes them preferable to weld neck flanges to many users.

However, the installed cost is not much less than for a weld neck flange because of the additional welding involved.