It depends a lot on the actual weather. If there is one good freeze, I will go out on 6". If there are any days where the temps get above 32 degrees, then I like to wait until its about 10" thick or so. I was on one lake last year where I drilled on hole at 10" thick ice, and then drilled 6 more holes in about a 100' line, and the last one was about 6". The ice was kinda popping, so I didn't go any farther out.