A flange hex bolt is a bolt that has a washer-like flange cast into the hexagonal head of the bolt. Designed to be used without the aid of a flat or locking-style washer, the flange hex bolt is manufactured to properly displace the torque and clamping force of the bolt over a wider area than that of a typical hex head bolt. Used a great deal in the automobile industry, this type of bolt allows assembly line workers to install the fasteners much faster than a comparable bolt and washer.
One advantage the flange hex bolt has over a comparably-sized non-flanged bolt is its ability to displace the clamping force of the fastener over a greater range. On soft, aluminum automobile engine components, the use of a standard hex head bolt could potentially crack and damage the area surrounding the bolt head. With this kind of bolt, the clamping force is displaced onto a greater area underneath the bolt head, thus saving the aluminum components. Valve covers, intake manifolds and water pumps are some of the aluminum components that often employ a flanged bolt head as a fastener. Other components of the automobile that benefit from the use of the flange hex bolt are the steering box, steering column and transmission.
Many metals are used in the manufacture of a flange hex bolt, from common mild steel to stainless steel and titanium, and each type of bolt has a specific use. For most applications on the automobile, mild steel is the metal of choice for the flanged bolt. This type of bolt allows for sufficient torque and will endure several tightening cycles that might otherwise fatigue other types of fasteners. Stainless steel fasteners are most commonly used in food-quality machinery and pipelines, as well as caustic areas that might serve to corrode a mild steel fastener in a minimum amount of time. Titanium fasteners are used in aircraft as well as high-performance applications where strength as well as light weight is required of every component.
Some applications of the flange hex bolt require a smaller-sized hexagonal head due to restricted space around the fastener. High-performance exhaust, such as headers, is one such application. The twisting and intertwined tubes of the headers make it difficult to tighten or remove a header bolt. Therefore, this type of flanged bolt uses a smaller hex-type head to allow more room around the fastener for tools.