Found this out there in internet land.
Origin of "Penny-wise" Nail Designations
There are two explanations for the English "penny" system of designating nails. One is that the eight-penny, six-penny, two-penny nails, etc. were so called originally because one hundred nails cost eightpence, sixpence, two pence, etc. The other theory says that one thousand eight-penny nails, for example, weighed eight pounds, one thousand four penny nails weighed four pounds, etc.
The "d" abbreviation for penny, (8d for example,) is of ancient origin and represents the first letter of the Roman coin denarius.
Nails used with wood, (such as wood siding nails, cedar shingle nails, etc.), are traditionally referred to by the "penny" designation, i.e., as 5d or 6d nails, etc.. However, nails for non-wood applications, (fiber-cement siding nails, metal roofing nails, etc.) are primarily referred to by inches, i.e. as s1 1/2", or 2" nails, etc. In our literature, the penny designation is listed first for those nails that are usually referred to by that term.
There is no readily apparent system for correlating the various penny designations. They must be memorized individually
Actually, for the siding industry, we do make odd size nails. 3d = 1 1/4", 5d = 1 3/4", 7d = 2 1/4", 9d = 2 3/4".
The odd size penny designaitions seem to fall on the 1/4" and most applications call for nails at the 1/2" increments. 6d(2"), 8d(2 1/2"), 10d (3'), 16d(3 1/2"). But get this -- ther are no 11d, 13d or 14d... weird.
Anyway, I hope you can use this info, and let me know if I can elp you further.
Paul @ Maze Nail (
http://coe.fgcu.edu/bengel/Nails.htm)