Attempting to do general maintenance cleaning the baffle screens. All three of the bolts holding the top baffle on were apparently over tightened on assembly. I only managed to get one out without breaking the head off. The broken bolts seem to be fussed to the threads. I've attempted multiple methods for removing the bolts with no success. I have drilled out the bolts exposing the threads on one, and still cant pick out the remaining bolt. I want to tap the original threads to clean them out. Anyone know the exact size tap?