These drill bits swiveled too much to make an accurate hole. The main problem is that the outside of the square bit is doing its best to turn as the bit turns, so you have to hold it with your hand.
Pros
Square hole diameter: 8 mm (5/16 in) and 9.5 mm (3/8 in) and 12.7 mm (1/2 in); Total core length: 200 mm (approx. 7.88 inches)