Barbed Coupling for all Rain Bird XF Series Dripline. Rain Bird’s 17mm barbed insert fittings are used with all Rain Bird XF Series Dripline, including XFD Dripline and XFS Subsurface Dripline. They have been redesigned and can now be installed over twice as fast as other barbed fittings. When you're installing the new XF Insert Fittings, you quickly notice that less force is required to securely attach the fittings. This will reduce hand fatigue and will save you time and money.