I have one of the above described tools, uses a 5/8" socket and you can do a one hand adjustment with the feeler gauge in your other hand. I also have a tool my dad made back in the 1920's that is a screwdriver with the blade set back into the handle and the metal cover is flush with the end of the blade, it is not as good as the purpose made tool, but is better than trying to keep a regular screwdriver in the slot with the rocker arm dancing.
