About half the strength of medium-strength bolts, these steel bolts are good for light duty applications. They are commonly used in tight spaces with moving parts, such as grain elevators and other belting systems, because the smooth, low-profile head provides a flush fit when installed. A square neck keeps these bolts from turning when tightening a nut. Zinc plating provides corrosion resistance in wet environments. Length is measured from the top of the head.