Standard bolts require a separate washer to protect the mating surface. A flange bolt combines both pieces into a single unit. The wide flange under the hex head spreads the clamping load evenly. This is useful when fastening components to thin sheet metal or aluminum engine blocks where stress concentration could cause cracking. They are common in suspension assemblies, oil pans, and water pumps. By reducing the parts count, they speed up repairs.
Mechanic Glossary
Flange Bolt
A high-strength threaded bolt with an integrated flat washer-like flange under the head, distributing clamping force over a wider surface area.
Frequently Asked Questions
No. The built-in flange is designed to replace washers completely.
Yes. They are commonly available in grade 8.8 or 10.9 for metric, and grade 5 or 8 for SAE, making them strong enough for high-load areas.
It has teeth under the flange that bite into the mounting surface. This acts as a lock washer to prevent loosening.
Only if you add a flat washer of matching diameter and strength. However, flange bolts have a wider footprint, so replacing them with the exact OEM bolt is safest.