Sorry to burst your bubble but ideas are cheap. Ideas are worth zero dollars. Everyone has an idea for the next Snuggy, the next Facebook, the next McDonalds. Having the money and knowledge to execute an idea is rare, and that is where the power lies.
If you truly believe you have a great idea, you need to partner with someone who has the resources to make that idea a reality. So you need to pitch the right people. If it’s a plastic/metal part, then you need to meet with someone that can fabricate that part.
So once you have that person(s), you need to break out an NDA (Non Disclosure Agreement) that stipulates they can’t steal your idea. Have them sign it. You will also need to give up partial ownership of the idea, because if they are gonna work on it or invest they need to benefit too. Perhaps even giving up 50% might be required, but ideally you never give up more than 49% of your company, so you are always in control.
Sorry to further burst your bubble, but people steal ideas all the time. So witnesses and your NDA are going to help out there. But don’t get too caught up in fear, 90% of the ideas out there are shit anyway, and it wasn’t going to make any money in the first place. Step one is producing the idea and making money, don’t get caught in the fear cycle or you’ll never get off the ground.
But assuming it’s a good idea, you find the right person, and the idea becomes a reality, and it makes money, then you and your partner(s) can all become rich. So invent a new doorstop or whatever it is the fuck you were thinking.