STAINLESS STEEL FLANGED HEXAGON BOLTS DIN 6921

Flanged Hexagon Bolts DIN 6921 — A flanged hexagon bolt builds a washer directly into the fastener: an integral collar beneath the head spreads clamping load over a wider bearing area than the head alone would provide, without needing a separate loose washer fitted during assembly. This plain-flange version has a smooth underside, which means it won't mark or bite into the surface it's clamping against — a genuine advantage on painted panels, coated sheet metal, plastics, or any finished surface where a witness mark from a serrated flange would be unacceptable. It's widely used in automotive and machinery assembly, HVAC and sheet metal fabrication, and general production-line joints where saving the step of fitting a loose washer speeds assembly without compromising the joint. Grade selection follows familiar lines: A2 is the standard choice for indoor, general-purpose assembly, while A4 earns its place wherever the finished product will see outdoor weathering, washdown cleaning regimes, or coastal and marine exposure — situations where a plain-flange bolt is often chosen precisely because it protects a coating that a marine environment would otherwise attack once damaged. The governing standard, DIN 6921, fixes the flange's diameter and thickness relative to the bolt's nominal size, along with the underhead geometry, so the built-in washer function is consistent across manufacturers and sizes rather than left to guesswork. Selecting the right bolt means treating the flange as part of the bolt's geometry rather than an add-on: clamp length calculations should account for the flange thickness in the stack-up, and flange diameter should be checked against the standard's dimension table for the size ordered to confirm it will actually cover the intended bearing area, particularly on slotted or oversized clearance holes. Where the surface finish doesn't matter and additional resistance to loosening under vibration is more important, the serrated version of this same bolt is the better fit.

FAQs
Do I still need a separate washer under a flanged bolt?
Generally no — the integral flange performs that role. A separate washer might still be added where a specific surface finish, electrical insulation, or extra bearing area beyond the flange's coverage is required for the particular joint.

Will a flanged bolt fit through a standard clearance hole, or does it need a bigger one?
The flange diameter is larger than the bolt's shank, so the clearance hole needs to be sized for the shank as normal, but the surrounding material must be flat and wide enough for the flange to bear fully — check this against the flange diameter for the size ordered, especially near edges or slotted holes.

Is the plain flange bolt suitable where vibration is a concern?
It offers some resistance through the increased bearing area and friction, but where vibration loosening is a real risk, the serrated version of this same bolt, or a separate lock washer, gives more reliable resistance than the plain flange alone.

Can a flanged bolt be reused after removal?
Yes, since the plain flange doesn't deform or bite into the clamped surface the way a serrated flange does, it can generally be removed and refitted without losing performance, provided the joint hasn't been over-torqued.