The reason why your trash can tapers. Most injection-molded objects have a slight taper for easy removal from their mold. This taper is called a draft angle. You see this design feature in everything from trash cans to phone charging blocks. However, some forms can't be helped by a taper. A plastic screw cap has threads that prevent it from being pulled out of its mold, no matter the draft angle. So, how do you make a mold for a screw cap that allows the part to be removed without damage? Let us know what you think in the comments.