I want to build a 3d-printed project case, but I'm wondering how to keep the power wire inside the case. I'll be creating an opening big enough to insert the power wire, but how do I keep it from coming out (like if someone pulls on it by accident). I have a lot of USB cables that have this big, round, grommet-like device on them. Is that something you can easily get and put around your wires yourself? What do people normally do for this?