This happens all the time. You're just finishing up hours of work when the nut for the last bolt drops, clanks, and is never to be seen again.

If the fastener is magnetic, you may have some luck just poking around with a magnet. These tools are pretty much a necessity for anyone working on cars. They come in all different shapes and sizes - all serving a different purpose.

If you have a magnet equipped with a sliding sleeve, you may want to pull back the anti-magnetic ring when your blindly searching.

Sometimes the part you dropped isn't metal, or magnetic. Your trusty pick-up magnet just won't do the job.

If you have a grabber tool, give that a shot. These will often be able to clench onto the rogue bolt easily.

Thanks to cell phones, tiny cameras are pretty cheap these days. There are several manufacturers that make cheap endoscopes you can hook up to your phone!

These tiny snake cameras will help you see where you can't. If you're not having any luck with a magnet, and endoscope can help you see exactly whats going on.

If you drop a bolt or part into the engine itself, you're about to have a bad time. Unlike air and fuel, metal bolts don't compress well inside an engine. In fact, they're more that likely to cause permanent replace-expensive-parts kind of damage. Under no circumstances should you start the engine if you think a nut or bolt is in the combustion chamber.

This includes dropping bolts into any part of the intake, exhaust, turbo, spark plug holes, intercooler, downpipe, cooling passages, or just about any open port into the engine.

In these situations, luck and a few good tools may save you days of headache.

First up, a tiny, flexible, telescoping magnet is your friend. You can likely slip this guy into an open spark plug hole to grab a bolt hiding inside the combustion chamber without having to remove anything!

When you're searching, think about how the engine is designed, and where the hole you dropped it in might lead to. Is it in the combustion chamber, oil passages, water jacket, stuck on top of a valve, or wedged in a valley somewhere? Follow it mentally and try to find it using your magnet tool.

If there's a chance it made it down to the oil pan, you may have some luck draining the oil pan

If you don't find it, you'll have to start removing parts off the engine to locate it. At this point you may decide to have the car towed to a shop to help you out. Whatever the cost, it'll be better then paying for a new long block.