Screw (or nail) size selection ?

[Maylinda]

I have a novice question - with the huge array of fasteners available, how do you know which type is the correct one to use? Is there a chart that says if the wood (or metal etc) is X dimension use Y screw? Obviously if you need to screw or nail through 3 2xW members you need a longer fastener - but how is the diameter chosen correctly.

in short - assuming all variables are the same, why would I use a #8 1" Screw versus a #6 1" Screw?

 

[chippie244]

The choice of screw size is usually down to common sense and practice depending on the materials to be joined and the use it is going to be put to.
Often the fitting will determine the screw diameter as only a certain size will go through the hole.
With wood usually screw through the thin material into the thick and go into the thick about as much as the thickness of the thin ie fixing 3"x1" to 4"x2" use a 2" screw through the 3"x1" into the 4"x2"
Most screws for general wood work will either be a 4, 6, 7, 8, 10 or 12 or metric equivalant. 4's are generally used in small hinges, 6's are used for door knobs and decorative fittings, 7's are for door hinges and window fittings, 8's and 10's are for general work with the 10's usually used over about 2 1/2", 12's are generally used for 4" or over.
This is obviously all very simplistic and there are many variations from this but it should help you get the gist of the subject