I have a JD 310B Backhoe. Why there are a few different styles of cylinders on the same machine, seems they would standardize them? Cylinders sized for the application of course makes sense. Stabilizers have the 'wire' ring , with thin threaded nut that's hard to get tools on to unthread,. Swing and crowd have a larger/thicker rod guide that's easier to grip with tools and a set screw in the outside of the barrel to hold the guide. Backhoe bucket is a thin rod guide and a set screw Boom appears to be thin threaded nut and a set screw, still have to get to it though.
I would find a parts manual and do some research to make sure all the cylinders on your machine are original. Some may not be. Whatever fits to get the machine up and running is usually the order of the day in the lives of these older machines.
JD did that for decades as far as I can tell. Seems maybe they transitioned more to the wire ring style from the other styles, but kept the swing cylinders unique style due to the difference demands of that application.
Because engineers like to make things complicated
That would explain the difference if it were the case, but the cylinder kits have fit based on the JD part numbers so it seems they’re all OE.