You have a couple pieces of wood you want to nail together. But what size nail should you use. What length nail should you use for a one-inch board? Two-inch board? And what is an 8 penny or 16 penny nail?

The accepted rule is to use nails that are two and one-half times the thickness of the wood you are nailing through. So, for one-inch thick lumber, use a 2-1/2-inch nail (or an 8-penny nail) and for two-inch thick material you’d use a 4-1/2-inch nail (or an 16-penny nail).

Here's how the "penny" system works: Nails that are sized based on the penny system use a number and a small letter "d". To figure out how long a nail is, divide the size by four and add a half-inch. Thus a 12 penny nail is (12 divided by 4=3), (+ one-half inch), makes it a 3-1/2-inch nail.