I made this tool to remove and install the spring. It has a 3/8" square drive on the back side.
I don't know the difference, I found the 930 spring would work by pure accident. I had the 930 torn down to fix the tip of the spring that would have most likely gouged the magazine tube. I also had the 935 torn down cleaning it and had both springs out and thought that this could be a problem if they weren't colored. We'll, brake cleaner removes the paint easily. I tried them in the 930 and the recoil was non-existent with the 935 spring and would not eject 2 3/4" target loads. I then tried them both in the 935 and the gun became 100% with 2 3/4" low brass target loads.
I sent pictures of the spring tip protruding into the bore of the barrel lug and asked if they would just send me the spring and they did.
This was back in the days of Maria answering the numerous calls from the Brian Eno's forum on ordering the non ported barrels. I don't know anyone answering calls there now.
Sent from my Tesla coil