A drill guide is used to eliminate bit wobble and ensure the beginning of your cut is straight. Once the cut is started it is a piece of cake. The bracket includes a level actuated suction cup to hold it securely in place both vertically and horizontally. The drill guide is adjustable up to 83mm bits.
I would definitely recommend adding these little guys to your tank. They are very playful and entertaining. My three were very healthy and quickly adjusted to my tank.
