Well, let's see now.
A captive spring is one that is held on the guide rod by a flange on the end. Kind of like a current factory Glock spring and rod.
A non-captive spring is one that just slides on oand off a guide rod. Kind of like my first generation Glock. Or my Colt. Or probably your Beretta.
A stainless steel guide rod is made out of stainless steel.
A tungsten guide rod is made out of tungsten metal.
Why? Because tungsten is denser than steel so the rod is heavier, which is supposed to reduce recoil. It will also reduce your bank balance because tungsten is much more expensive than steel.
The screw and circular thing that came with the replacement spring are probably to go on the same brand of guide rod to keep the spring captive.
Question: Is the replacement spring flattened wire like the Glock factory spring or is is ordinary round wire? If it is flat wire, you can take the front end flange off the plastic Glock rod by yanking, it just snaps into place. If round, you probably would do better with a steel rod meant for round wire springs. I'd have thought the spring vendor would have them. Call him up.
