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Sometimes, usually due to using the wrong size of staples, the top of the stapler and the stapler tray might get stuck together. To unstick them, create a fulcrum out of a long, thin object, like a big paperclip (a heavy-duty one will work much better than a small, plastic one) or even a letter opener. Insert the object where the top and tray meet, and gently push the fulcrum down to pop the pieces apart. Be careful while you do this. If you use too much force, the thin object could slip and scratch you. Anytime you have a jam, especially if you've recently reloaded your stapler, take a moment to check with the manufacturer's specifications regarding staple size. Surprisingly, there are a lot of different sizes out there! Check the box of staples again the specifications to make sure they match. Thankfully, most stapler manuals can be found online, so don't worry if you've misplaced yours. Just search online for the brand and model of your stapler. Generally, most staples can fasten together 20 sheets of paper, but your brand might be able to handle more (or perhaps less) than that. Your model's instructions should specify what that maximum number is. If you need to staple together more than that maximum-sheet limit, you'll probably need to look for an industrial stapler. Lots of libraries have these available for their patrons to use. If the trays aren't lining up properly, or if they're blocked by excessive dust or scraps of paper, that could cause recurring problems. You could use a can of compressed air to clean away dust, or use a screwdriver to tighten the metal parts so they fit together correctly once again. If your stapler feels loose or jiggles easily when you shake it, chances are something needs to be tightened. If you need to or want to, try taking it apart to really see how everything is working together. If you've checked the different things that can cause a stapler to jam and your stapler still isn't working correctly, it may be time to invest in a new one. Thankfully, staplers don't have to be expensive, and if you work in an office, chances are your human resources department will pay for a new one for you. Remember, when you get your new stapler, put the instruction booklet somewhere safe so you can refer to it in the future.
Use a thin object to separate the top from the bottom if they're stuck. Check that you're loading the stapler with the right size of staples. Avoid stapling together more than the maximum-sheet capacity. Check for blockages between the stapler tray and the top spring section. Replace your stapler if you can't get it unjammed.