This 20 PSI pre-set regulator is made to go on a 1/2" sprinkler riser. Has built in check valve, so will not create run off. Valve opens at 25 PSI on start up and shuts off at 10 PSI on shut down.
No change in threads as it screws on the 1/2" male threads and ends in 1/2" male threads.
This comes in play if you have a very large single zone and you need to keep the pressure high within all the PVC piping but bring it down before you get to your drip components connecting to the 1/2" riser.