I tried searching for this but didn't find what I was looking for so here goes...

Is it necessary to clean the threads when changing spark plugs? If so can anyone recommend an easy, cheap way of doing it?
Regarding the gap, my manual says to use a wire type tool, not a blade type, to measure and set the gap, which I've never seen. Does it really matter? Is a blade type really that inferior?

Any input would be appreciated.