STAINLESS STEEL SERRATED FLANGED HEXAGON BOLTS DIN 6921

Serrated Flanged Hexagon Bolts DIN 6921 — Take the same integral-flange geometry as the plain DIN 6921 bolt and machine radial serrations into the underside of the flange, and you get a fastener that actively resists loosening rather than simply relying on friction from applied torque: as the bolt is tightened, the teeth bite into the mating surface and create a mechanical key against rotation. That makes it a common specification in automotive and machinery assembly, chassis and engine mounting points, and any joint subject to sustained vibration where fitting a separate lock washer or thread-locking compound would add an assembly step. The trade-off is straightforward — those same serrations will mark softer metals, coatings, or painted finishes, so this version is best reserved for joints where the clamped surface is bare or unfinished steel and appearance isn't a concern. Grade selection follows the same pattern as most vibration-prone assemblies: A2 suits general indoor machinery and equipment, while A4 is worth specifying wherever the assembly will see road salt, washdown chemicals, or coastal exposure, since a serration-damaged surface loses its protective coating and becomes a starting point for corrosion that A4's molybdenum content resists far better than A2's. The standard, DIN 6921, controls flange diameter, thickness and the serration pattern itself, so the bite and bearing area stay consistent regardless of manufacturer. Choosing the right bolt means accounting for the flange in clamp-length calculations exactly as with the plain version, and checking flange diameter against the size ordered to confirm adequate bearing area over the clearance hole. Because the serrations wear down with repeated use, this bolt is best suited to joints that are torqued once and left, rather than assemblies that are regularly stripped down and rebuilt — for frequently serviced joints, a plain flanged bolt paired with a separate lock washer generally holds its performance better over multiple reassembly cycles.

FAQs
How many times can a serrated flanged bolt be retightened before losing effectiveness?
There's no fixed number — it depends on torque level and surface hardness — but each reinstallation embeds the serrations into a slightly worn pattern, so a joint expected to be serviced repeatedly is better served by a plain flange bolt and separate lock washer than by relying on serrations indefinitely.

Does the serrated flange replace the need for thread-locking compound?
In many vibration-prone joints, yes, the mechanical bite is enough on its own; in higher-vibration or safety-critical applications, thread-locking compound is sometimes still specified in addition, as a second line of defence rather than a replacement for the serrated flange.

Will the serrations damage a painted or powder-coated surface?
Yes, that's their intended function — biting through a coating is exactly how they generate resistance to loosening, so this bolt should be avoided wherever an intact painted or plated finish must be preserved on the clamped face.

What's the practical difference between this and simply using a spring washer with a plain bolt?
A serrated flange bites directly into the mating surface at the moment of tightening, giving immediate resistance without a separate loose component to fit or lose during assembly, whereas a spring washer relies on its own compression and can be omitted or misplaced on a busy production line.