Product Details:

Use the CRL Tapered Plug for drilling your second hole in receptacle outlets. Made of a special rubber compound that won't break the glass if dropped on it accidentally. Easy to use: just insert it in your first hole so your coolant won't leak out during the drilling of the second hole. Normally used with the CRL Suction Base Drilling Rings.
Always wear the proper safety gear including gloves and eye protection when drilling glass. Work should be performed on a flat, horizontal surface. A Ground Fault Circuit Interrupter must be used when using any type of electric tool in conjunction with water or coolant. Failure to follow any of these precautions can result in operator injury.