Drilling pilot holes, what size drill for what size screw? - Model Railroader Magazine

The all in one's are a great resource. generally, they're made for drilling holes in wood for wood screws and work well for that.

jj and Roger offer up suggestions to consider. Most of the time we use a drywall screw of some sort on benchwork these days. This is a different screw than a wood screw, but we won't pursue technical differences, just note that this can sometimes require a different pilot hole size. The hard vs soft wood thing has been mentioned already. But you can also get screw with different threads, fine or coarse, in basically the same screw size. In some cases, you don't want a supertight fit; in others you do.

With drywall screws, I usually use a bit that is as close in diameter to the body of the screwthreads as is possible. A little bigger hole is OK most of the time, but could make it easier to strip out. Too small and it is a PITA  to get in.

For standard wood screws, the charts usually work, but sometimes need a  little adjusted for all the reasons I mentioned and some I may have forgot. A chart that has different listings for hard and soft wood is often helpful. If no difference is noted, they often are for softwood and you may need something slightly bigger in hardwood.

I generally bore full depth for the pilot hole. In some case, leaving the last 1/2" or so undrilled in softwood works well and gives a fit more resistant to loosening. Yes, you can skip the pilot hole in softwood, but you'll find a lot of splintering, depending on what and how you do things. Pilot holes take a little longer, but tend to give more reliable, superior results.

 Not directly related to the drill size, but using the square drive head gives you superior control over running the screw in or out. It can give you more grip to let you use a smaller diameter pilot hole, for instance. I use 'em because I have a bad shoulder and rarely drive nails.