Twist drills grab in thin material and drill three-lobed holes and can distort the material where you want it to be flat at the seal. 20mm is a bit small for a Greenlee style punch. Even a cheap one is better than nothing. What tools do I use to drill clean holes in both the plastic and aluminum enclosures so that the cable glands fit snugly without any gaps? I tried searching for M20 drill bits and thread taping, but couldnt really find anything solid. There are several types of electrical panels, including: Breaker panels: These panels use circuit breakers to interrupt electrical flow when a circuit is overloaded or experiences a fault. Helping you become a better technician and passing out high. There are four main ways to drill a push button hole, three of which I recommend. There are two popular size push buttons.