SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I inherited a sprinkler system in our lawn for a house we purchased and have been working on it most of the summer to get it working correctly. So first off a big thanks to all who have posted here and to Sprinkler Warehouse for being incredible resources through my trials! I've replaced valves, diaphragms, solenoids and now am getting to replacing and raising many, many sprinkler heads.

The system is probably around 10-12 years old, and I have found that I-20's were used for most of the heads. I'm finding that most of these are leaking now, and/or have the wrong size nozzles installed. However many of these have a different nozzle than the new I-20's I have recently purchased. The older ones are red and are completely round. The new are either blue or gray and are square on top. Was just curious if these old ones are just that, old? Or is there a nozzle that would fit them? They look a lot like what I think are PGP nozzles, but are definitely I-20's as it's stamped on the top. Replacing a few of these nozzles would help the pocket book rather than having to replace the entire head.

TIA!