POWERTEC 70189 Y-Fitting, 6 x 4 x 4" Reduces down from a 6-inch port, or mainline, to dual 4-Inch branches Enhances dust-collection system airflow and efficiency Ability to branch to multiple machines from system mainline Tough, durable ABS plastic material 6-Inch nominal end measures 6-23/64-Inch O.D. and 6-Inch I.D. Both 4-Inch nominal ends measure 3-61/64-Inch O.D. and 3-23/32-Inch I.D.