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This top barrel is designed to replace the original orange barrel tip of a Nerf Star Lord Quad Blaster. These barrel tips render the gun incapable of firing Nerf darts, but also still allow the gun to open and close bec ause I thought that was a really neat functionality of the base Nerf gun. You can use the same exact screws you removed from the original orange tips to affix these replacements.
Some modifications to the base blaster are required to fit the top barrel into place. Specifically, you will have to trim some of the inside of the barrel cover (the part that moves) away. I did this with a Dremel, and would recommend you do the same - it makes it a lot easier. The barrel is designed with two 5mm holes to accommodate LEDs. How you go about doing that is up to you, but I've discovered the best effects (in my opinion) can be obtained by filling the barrels with clear resin to help diffuse the light fully down the barrel. You could also try lightly sanding some clear acrylic with a high-grit sandpaper and cutting it to shape to fit inside the barrel.
I originally made these models to print on my Makergear M2, which prints at 100 micron (.1mm) resolution. They fit right onto the nerf guns straight off the print bed. I'm assuming Shapeways has a good enough print fidelity that you should be able to put these parts straight on your own nerf gun, but be aware that you may have to do a bit of sanding to get a proper fit.