Metric Flange Bolts are serrated whereas Frame bolts are not. Flange bolts are available in a wide range of sizes both metric and standard. They are available in both steel and stainless. A flange bolt is used much like a cap screw, except it has a built in locking mechanism under the wide hex washer head. When not going into a pre-drilled hole, they are typically used with matching serrated flange nuts.