Has anyone seen a reasoned discussion outlining rules of thumb for specifying wood screws. Clearly there are screws like a #12 that is 1/2" long that approach being ridiculous. Likewise a #2 screw that is 1/2" long has a likelihood of breaking under load.
Today I am faced with specifying a 5/8" long wood screw to draw together a lapped joint in birch. A #6 screw gives me 18 threads/inch, a #8 gives 15, and a #10 gives 13. Assuming the tip of the screw penetrates 5/16", I have 5.6, 4.7, or 4.1 threads engaged. In the process I trade off a smaller root for more threads or fewer threads for a larger root diameter. I'm interested in an engineering based rule of thumb for specifying the screw size for a given length.
Thanks
baumgrenze