Another way a lot of 1 piece guide rods work, is that they have a hole in them that is visible when the slide is locked back. You lock the slide open, insert a bent nail/paper clip/wire into the hole, let the slide slowly go forawrd. The nail prevents the plug from moving foward to the end of the guide rod but allows the slide to move.
In essence, this gives you a captured recoil spring once top end is removed from the frame. To remove the spring you must further depress the plug & spring, remove the nail/clip, then ease the plug off the guide rod, all without shooting the spring across the room, slipping and jabbing yourself in the hand, swearing & cussing until your wife walks in wondering what's going on....
YMMV, but 1 piece guide rods SUCK!!! (IMO of course)