I used a 30mm Forstner bit since 28.5mm is kinda tough to find. It worked great. Its a tiny bit bit bigger than the 1 1/8" that everyone recommends, but only by about 1/16. I used this cause it was in the set of forstner bits that already had and I didn't want to go out and buy another special bit.
If you are going shopping for a bit, I would get a forstner bit over a spade bit, it makes cleaner holes.