sigma693, the riser usually threads into a threaded tee installed into the zone line. The riser is made from material which will flex or even break when subject to shock. It appears that there is a slip tee instead. My best suggestion is to use 'funny pipe' for the riser. It will absorb shocks and reduce the chances of the tee (and zone line) breaking. The pipe can be glued directly into the tee and you can glue a male adapter at the top end to accommodate the sprinkler head. And, just to cover all bases, make sure that all the components are correctly sized for each other.