Then I ran out of bigger drill bits and I had to realize that you can't just walk into a hardware shop hoping to find a 18mm drill bit. But I did find 17 and 19mm hole saws. Initially I thought, 17mm would be too small and I bought the 19mm bit: As my hole was already 12.5mm the normal auger for it with the little pilot drill bit would not have help me. But when I tried to drill that hole I was afraid that the hole would get too bit and possibly damage the transfer box...