These are machined with a profiled radius on the inside to increase flow.
Standard weld on's are drilled straight through and parted off.
999-06-DF (-6 Male Flowed Aluminium)
999-08-DF (-8 Male Flowed Aluminium)
999-10-DF (-10 Male Flowed Aluminium)
999-12-DF (-12 Male Flowed Aluminium)