I have a situation where two knives on my portable 12" planner need to be flipped in order to use the other cutting edge. Each of these two blades is held by six bolts for a total of 12 bolts with recessed hex heads. The tool included an attached long-handled Allen wench for the job.
I was able to loosed all but three of the bolts and could not, for the sake of me, loosed those three. I read on line about the best product for lubrication to loosen stuck bolts like my situation and ordered a small can of Kroil Penetrating Oil. I was pleasantly surprised with the smell, and the smooth consistency along with the easy application: it just flowed out.
Sure enough, those three stubborn bolts gradually loosed for me. I recommend this penetrating oil for anyone having a difficult time trying to remove bolts as I did. Even though my planner is kept indoors and showed no signs of rusting, I'm sure Kroil will work even on rusted hardware!