The best wrench I have found to remove the 4 little fan bolts to water pump, is the Craftsman fully polished set. the 10mm box end is very thin and works well.
also the Snapp-on 10mm might work well also.
the normal Craftsman box end is too thick to work.
X2 on rounding off the bolt heads with an open end. It might work on a couple, then there is the one that is stubborn.
Charlie