Oxy-actelenye red hot, then six point ¼" drive socket or six point box wrench. The box wrench lets you see if it is twisting off or turning. Buy a new bleeder screw when you get it out and use anti-seize on the threads. The little rubber caps also keep moisture from getting in to rust them from both sides. I buy lifetime calipers now and just get them replaced free. Last ones on my plow truck were so rusted all the flats were gone and no wrench was going to fit.