You're kidding, right? If you honestly think we are going to know which one of the hundreds of screws in the engine, transmission, body sheet metal, head lights, wipers, and exhaust system you are referring to, you'll have to post a close-up photo of it. Even then we probably won't know the size you want to know. We try different wrenches until we find the right one to fit the head. We rarely need to know the thread pitch; we just find a bolt with the same pitch or that fits the same nut. As for length, we either measure it or match it up to a replacement.
If you don't have the old screw to look at, find one from a similar model in a salvage yard. You'll be guaranteed it will be the right length, diameter, thread pitch, and hardness as what you're missing.