The Plastic Sprinkler Spike 15mmFI is a perfect solution for that temporary irrigation system you have been talking about.
The Plastic Sprinkler Spike comes complete with a 20mm screwed cap on one side (this screwed cap is remove-able to be able to use the 20mm male thread) and a 20mm female screwed thread on the other side. The top of the fitting has a 15mm female thread.
Please note, if you are intending on using this product in conjunction with a Rain Bird Nozzle or Hunter Nozzle, you will require the two products which are listed below.