Flange Bolts

Flange bolts combine a hex head with an integrated washer-like flange beneath it. The flange spreads clamp load over a wider area — eliminating the need for a separate washer — and serrated versions bite into the surface to resist loosening. They speed assembly and improve joint reliability, making them popular in automotive and machinery work. We stock flange bolts in serrated and smooth, across grades and materials.

Serrated vs. Smooth Flange

Serrated flange: ribs on the underside bite into the bearing surface, providing anti-loosening grip similar to a lock washer — ideal for vibration-prone joints. Smooth flange: a clean bearing face used where the surface must not be marred, or on softer materials. Serrated is the more common and the stronger anti-vibration choice.

Why Flange Bolts

By building the washer into the head, flange bolts cut part count and assembly time and guarantee the bearing surface is always present. The large flange also distributes load on slotted or oversized holes and soft materials better than a plain hex bolt.

Grades and Materials

Grade 5 and Grade 8 steel for general and high-strength work, typically zinc plated. 18-8 and 316 stainless for corrosion resistance. Metric flange bolts use classes 8.8 and 10.9.

Dimensional Standards

Metric hex flange bolts follow DIN 6921; inch versions follow IFI and ASME flange bolt standards.

Selecting the Right Flange Bolt

Choose serrated flange for vibration resistance, smooth for surfaces that must not be marred. Match grade to clamp load, finish to environment. Note that serrated flanges should not be used where the bolt must be frequently removed or where surface marring is unacceptable. Verify thread pitch matches the nut or tapped hole.

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