These grade 2 round head carriage bolts by Precision(R) are made with galvanized steel. They have a 5/16"-18 thread and are 6" long. Sold in boxes of 25 bolts, they come without nuts. The hot-dip galvanizing of steel allows for one of the highest degree of corrosion resistance amongst all mechanically-plated fasteners. This protection is ideal for outdoor applications, such as decks, fences, and more.