Your drain stopper in your bathroom sink has broken. You can no longer place a plastic/chrome pop-up stopper to be connected to a rod inches into the drain. The metal or plastic protrusion rod is no longer visible in the drain. It broke off and fell into the drain pipe (e.g., the P-Trap). How do you fix this problem with replacing the fewest amount of tools and parts?
Buy a ball rod assembly that has different size balls. This is a ball-and-socket mechanism. You won't need other wing nuts or pipes. You just need a drain ball rod assembly. You can buy one here: DANCO (88532) Universal Pop-Up Drain Ball Rod Assembly
To learn more about how to replace it and other parts of a pop-up drain in a bathroom sink, see this video.