This is what I use. We Brits call it a combined ring spanner/open-ended spanner (is this what you guys call a box wrench?). I use the ring-spanner end; it's offset so when I get it on it sticks out away from the caliper and then holding it in the direction to undo the bolt so that there is no slack I give it a good whack with the hammer (like JRSIII).
this second photo shows offset
