Holman's range of 4mm Riser Tube is ideal for connecting 4mm micro irrigation from the main supply line. The low density polyethylene (LDPE) material provides a strong, reliable grip onto 4mm threaded fittings. Riser tube is predominately used to run from the main poly pipe water supply line, vertically up an irrigation stake to mount either a micro jet or micro spray. The rigid material helps keep these sprays in place. Create a micro irrigation system to run and throughout your garden beds. The connection between the rigid tube & the 4mm fitting, is most important. This connection must be threaded. The 4mm thread bites into the rigid tube to connect. A 4mm barb can not be used.