Spark plugs are simple things. People wax eloquently forever on which one to use. However, that is a waste of time. The choice of match does not make a bigger bonfire. That being said, a bad match might not light it and some plugs types will last longer than others.  For this reason, spark plugs should be checked and changed regularly. Over time the spark plugs electrodes will wear, chnaged the all important gap that shapes the spark. Over a long period, if not changed the spark plug threads will fuse with the motor threads. This will often strip the motor's threads requiring a helicoil (if you are lucky) or a new engine head (s).

Installing and removing plugs are a trick as well. If you use the wrong tool, the possibility of breaking the plug is very high. The proper tool is called a spark plug socket and they come in sizes that match all spark plugs types. They are made for this task and have a foam, silicone or rubber insert that protects the plug from shattering. They look different in Europe so I have provided a picture of both types.

I carry one in my Morgans. Other spark plug questions are addressed in the Ignition Section.