Here is another photo of the counter bore tool. It has an 80 degree included angle to it. I have tried a single cutter bore and found it to not work as well. Just be careful not to remove any more material than necessary to give a good seal with the for mentioned grease gun fitting. Before greasing poke a nail in the center hole a few times to loosen up the spring loaded check valve. I would not remove the rollers from the grousers to lube them. The bolted up assembly holds the metal shield tight to the roller. If you grease first, the grease may keep the roller from coming up tight against the grouser and then be loose after driving a while.