What Jim said (especially about sticking with the OEM plugs) but the hex bit is 5mm (to answer the question marks). John linked my site and I show how to replace them with the wheels off but you don't have to take the wheels off in order to change the plugs. I do a brake inspection at the same time so it's just easier for a fat guy with fat hands to reach in through the wheel well.
I have the OEM part number for the Bosch plugs on my site if you want to look around and find them online.
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