You'd think that thick metal bolts would be fail-proof, yet the threads and bolt head can quickly deteriorate if you don't handle the bolt correctly. Stripped heads and threads can make the bolt nearly useless. If you're dealing with a bolt that appears to be stripped in some way, you have to remove the bolt and see if you can repair it. If it's not repairable, then you have to replace it -- you can't leave a stripped bolt in place. If there is an emergency where you have to dismantle the equipment with the bolt, you won't be able to remove it as quickly as you need to if you can't get a good grip on it.
Creating Friction for Stripped Bolt Heads
To remove the bolt if the head is stripped, you need to create friction. When the head is stripped, the metal screwdriver you're using simply slips past the metal grooves in the head. So, what you want to do is create friction. (Of course, if the bolt has a raised head with sides that you can grip with pliers, then you can just use those to turn the bolt, but friction is your friend for flatter bolt heads.)
A thick rubber band can provide the necessary friction. Place the rubber band over the bolt head and pin it down with a screwdriver that's slightly larger than the stripped area. Press down and try turning to release the bolt.
Restoring or Creating Threads
Whether you've got a bolt that has rusted threads that no longer grip the inside of the bolt hole, or bent threads that no longer match the threads inside the hole, you may be able to repair the problem. Cutting and rethreading dies help restore bolt threads. Cutting dies actually cut new threads in bolts, while rethreading dies can remove debris and rust to clean out existing threads. You can try using these to see if you can make the bolt usable again.
Sometimes you can't restore the bolt, such as when cutting new threads would weaken the shaft of the bolt. In these cases, you need a new industrial fastener. It helps to clean out the bolt hole if possible and to re-measure to ensure the new bolt fits correctly. Your attempts to get the bolt out before could have widened the bolt hole a bit if it was in a softer material like wood.