13mm

This includes the black connecting pipe, plugs to end the line, clips and pegs to secure the hose, T Joints and L Joints for system construction, spray nozzles, sprinklers, drip heads 

To prevent unnecessary loss of water pressure it is best practice when building a micro-drip system that you use the widest, thickest pipe as much as possible and only branch off from the 13mm pipe to a smaller pipe when you are close to or at the point of watering.