Whatever your project, there is a screw or nail for the job. You need to understand how these fasteners are sized so that you may determine which type best suits your application.
Nail sizing method
Nails are sized by length. The unit of measure is called a "penny" and is expressed with the lower case "d." As the nails get longer, the gauge (the thickness of the shaft) gets thicker.
Nail sizing begins at 2d, which is 1 inch long, and increases sequentially by one through 10d. Generally, each "penny" through 10d increases in length by 1/4 inch. After 10d, nails progress to 12d (3 1/4 inches), 16d (3 1/2 inches), 20d (4 inches), 30d (4 1/2 inches), 40d (5 inches), 50d (5 1/2 inches) and 60d (6 inches).
Nail counts per pound
Nails are sold by weight. You can expect approximately 850 nails per pound of 2d nails; 540 of 3d; 300 of 4d; 250 of 5d; 160 of 6d; 150 of 7d; 100 of 8d; 90 of 9d; 65 of 10d; 60 of 12d; 45 of 16d; 30 of 20d; 20 of 30d; 17 of 40d; 13 of 50d, and 10 of 60d.
Screw sizing method
Screws are sized by length and gauge. They usually are 1/4 inch to 4 inches long and have a gauge between 2 and 24. The larger the gauge number, the larger the screw. Therefore, a box of screws labelled "3/4-10" indicates a 10-gauge, 3/4-inch-long screw.
Screw counts per carton
Screws can be sold by either weight or quantity. Typically, you can expect to purchase speciality screws (such as self-tapping and sheet metal screws) by a specific count, and bulk construction screws (such as decking and drywall screws) by the pound.