I purchased a house recently that has a Hunter irrigation system (Hunter Pro-C controller with Hunter Pro-Spray heads). One of the heads had the nozzle with the top section of the riser(?) pop off. I attempted to screw this back into the part of the riser inside the head. It tightens down some and seems to be secure but if I pull on it with a bit of force it comes apart. I can't tighten it down beyond a certain point or it loosens. I assume that the threads are stripped? What could I do to fix this? Replace the head? And if I do will the riser piece come with it so that I can just attach the old nozzle to the top?

Thanks in advance for any help with this.