This is one of those "must-have items" for your spare parts kit, if you are a 1911 owner. Having a spare plunger & spring assy. will put you in good shape to fix several potential problems. The obvious one is a lost part. Sooner or later, you're going to remove a thumb safety and as you pull it out of the frame, you'll see something go flying off to one side, often to disappear forever. If you have a spare you can keep on going with what ever you are doing and not have to stop to search for the lost part, or wait for days for another to be sent to you.
Having one of these plunger & spring assemblies on hand also leaves you ready for preventive maintenance as the plungers and springs are all items that wear out with use and don't get addressed until you start having functioning issues with the slide stop and thumb safety. The ends of the plungers are supposed to be domed, but the tips will flatten over time. The plunger spring will definitely loose tension over time. It's definitely a group of parts that need periodic replacement.
You may have noticed that our springs have a slight "kink" in the middle of them. This is actually supposed to be there to prevent the plunger assembly from flying out and getting lost as we mentioned earlier. The only way to get a spring with the correct kink is to learn the right way to put that kink in without damaging the spring's strength and we have done that for you.