MOOSE. Please stay away from anything that even looks like a stone. All it will do is melt the plastic, and make one hell of a mess.That being said, the very thin cut off wheels (abrasive base) can have uses on plastic, but this is not one of those.I would use a combination of 9901, 9903, and 9910. I chose those because they cutting area of the bit is the same diameter as the shank so you will have less chance for that to get in your way. Please use medium speed and make very light cuts. Try and make your cuts so the cutter is wanting to climb out of the cut. This is usually backwards but because of how soft the material is and the depth at which the product will be destroyed, it could save your cap if the cutter decides to grab.