source: this website
Hobbyists, prototype builders and engineers may have to deal with tough choices: which screw size should I choose? how tight should it be, and which load can it bear? what’s the best thread size for my application? Luckily, this website provides a set of basic rules and definitions, a sort of handy guide with useful terminology and hints about the choice of screws, bolts, nuts etc.
For instance, Wood, Sheet Metal and Drywall screws differ from Machine ones; the screw head type depends on the application; the screw thread could be coarse or fine, according to the accuracy requirement. Sizing a screw for a given load would seem to be a simple matter, but a set of basic rules exist and it is reasonable to abide as much as possible by them. Did you know that, in most situations, the ground acts as a spring? I did not… Another nice thing is the guide for picking a screw or bolt for a given load, as well as the computation of how much thread engagement is needed. Material choice, the use of washers and other locking methods are also discussed. No doubt, this webpage is worth a visit! 🙂