Single-use conical spring washers in steel. When tightened, they flatten almost completely, generating a residual stress that maintains the clamping force against relaxation, settling and thermal variations.
DIN 6796 washers —also called Belleville washers or conical spring washers— are fastening elements with a frustoconical geometry, manufactured to the German standard DIN 6796 “Conical spring washers for bolted connections”.
Their specific job is to secure bolted joints. Once the joint is tightened, the washer is almost fully compressed and permanently exerts a residual axial force that compensates for bolt elongation, thermal expansion and the micro-settling of the mating parts.
It is important to distinguish them from the DIN 2093 / EN 16983 disc spring. Although they share the conical geometry, they are not interchangeable: the 6796 is a fastening element with a very short travel; the 2093 is an elastic spring.
They share the conical geometry. Confusing them is one of the most common application errors in technical fastening. This table summarizes the difference, column by column:
| Criterion | DIN 6796 · Belleville | DIN 2093 · disc spring |
|---|---|---|
| Function | Fastening element · permanent elastic locking | Elastic spring |
| Elastic travel | Very short · nearly flattened when tightened | Long · designed for controlled deflection |
| Configuration | A single piece per bolted joint | Stackable in series · parallel · mixed |
| Force precision | Reference (not exact) · works at very high stress | F/s curve calculable with precision |
| Typical location | Under the bolt head or nut | Hundreds of different applications |
Standard catalog DIN 6796 washers cover nominal bolt sizes from M2 to M125. The standard defines the geometry (diameters, thickness, height), the mechanical behavior (flattening and residual force) and the applicable tolerances.
| Parameter | Meaning |
|---|---|
| Dᵢ | Internal diameter · H14 tolerance. Compatible with the bolt Ø (M2 — M125) |
| Dₑ | External diameter · h14 tolerance |
| t | Material thickness |
| h max | Maximum initial height · before the first compression |
| h min | Minimum height after compression · after the first compression |
| F flat | Flattening force (N) · load needed to fully flatten the washer |
| F res | Residual spring force (N) · minimum guaranteed load in the tightened joint |
The F flat and F res values in catalogues are reference values, not individually guaranteed.
The actual force depends on the batch hardness, the geometric precision and the friction coefficient at the contact surface. The force tolerances are wide by design: the 6796 works in a very high stress range (420–510 HV) and the effective residual force comfortably exceeds the range of a conventional split lock washer at any point in the band.
The DIN 6796 is placed between the bolt head (or nut) and the surface of the part. When the joint is tightened, the washer becomes almost fully compressed. Its outer rim (Dₑ) bears on the part; its inner edge (Dᵢ) stays in contact with the flat face of the head or nut. The cone flattens toward the center of the joint, exerting the residual force permanently.
Tell us about your use case and our engineering team will help you choose the optimal solution.
DIN 6796 washers are made from C60 spring steel or higher for most applications. Where the environment demands it — corrosion, cryogenics, high temperature — stainless steels and Inconel 718 are also available.
Catalog standard. Hardened and tempered to 420-510 HV: it covers virtually every application when paired with the right coating.
For environments with condensation, sheltered outdoor exposure or industrial settings with high relative humidity.
It retains its mechanical properties at very low temperatures: this is the choice for cryogenic applications.
High temperature and highly corrosive environments, where stainless steel is no longer enough.
The modulus of elasticity of stainless steels and Inconel is lower than that of standard C60. For the same geometry, the residual force in stainless steel or Inconel is somewhat lower than in carbon steel. Where the environment allows it, compensating with a coating is the optimum solution both technically and economically.
The base material (C60 spring steel or higher, stainless 1.4310, cryogenic stainless 1.4568 or Inconel 718) determines the intrinsic corrosion resistance and the allowable temperature. For carbon steel — the most common choice — the coating is the main protective barrier. These are the coatings available at Surisa:
| Coating | Protection | NSS · ISO 9227 | Typical application |
|---|---|---|---|
| Manganese phosphate | Low–medium | — | Storage · transit |
| Mechanical zinc plating | High | Depends on thickness | Outdoor |
| Geomet 321 | Very high | 720 h salt spray | Automotive · wind power · outdoor |
For mechanical zinc plating, salt spray resistance depends on the coating thickness:
| Thickness | Salt spray · white rust | Salt spray · red rust |
|---|---|---|
| 5 µm | ~24-48 h | ~120 h |
| 8 µm | ~48-72 h | ~200 h |
| 12 µm | ~72-120 h | ~300 h |
| 25 µm | ~200-240 h | ~500 h |
The DIN 6796 washer appears in any bolted joint that needs to maintain clamping tension against vibration, thermal cycling or micro-settling of the parts. These are the sectors where Surisa supplies it most often:
Safety fasteners subject to continuous vibration. The 6796 replaces the flat washer + split lock washer combination with a far higher residual force and without damaging the contact surface.
Joints subject to dynamic loads and critical vibration. Vibration loosening is one of the main risks: the constant residual force of the 6796 prevents it throughout the turbine's service life.
Equipment with dynamic loads that affect static joints. It maintains bolt tension against the progressive micro-settling of the mating parts.
Fastenings exposed to wide thermal cycling, continuous vibration and infrequent maintenance. The 6796 maintains clamping force between interventions.
Joints subject to daily thermal cycling and traffic-induced vibration. It compensates for bolt elongation caused by the expansion of the structural parts.
Combined with stainless steel or coatings with high salt resistance, it maintains its elastic locking function in saline environments and under continuous sea spray.
With a material suited to the fluid and the process temperature (stainless steel or Inconel 718). It keeps the joint sealed against thermal expansion of the piping and pressure cycling.
Where the conventional split lock washer has proven insufficient, the 6796 is the direct upgrade: same location, several times the residual force, no surface damage.
They share the conical geometry. The DIN 6796 is a static-use washer that guarantees, after its deformation, a remaining contact force that prevents the joint from loosening. The DIN 2093 is an elastic spring, that is, it can work cyclically: it can also be stacked in series or in parallel to achieve the desired Force vs Deflection curve. They are not interchangeable: using a DIN 6796 as a spring, or a DIN 2093 as a fastening element, are application errors.
No. The DIN 6796 standard is intended for use with a single washer per bolted joint, placed between the bolt head (or nut) and the surface. If the application requires elastic stacking —for example to achieve greater travel or to tune stiffness— the correct element is the DIN 2093 disc spring, which is indeed designed for series, parallel or mixed configurations.
Yes, and with advantages. A DIN 6796 exerts a residual force several times higher than that of a split lock washer (DIN 127) of the same nominal size. It also does not damage the contact surface the way toothed lock washers do, and it maintains tension throughout the service life of the joint, not just at the moment of initial tightening. That is why it is the preferred element in critical and vibration-prone joints.
For both DIN 2093 and DIN 6796 we offer manganese phosphating for transit and storage, mechanical zinc plating for outdoor use —its protection depends on the deposited thickness— and GEOMET 321 for applications that require maximum protection outdoors. Ask us about other treatments.
Yes. Beyond the standard M2 to M125 catalog range in C60 steel, we manufacture DIN 6796 washers in non-standard sizes, in stainless steels (1.4310, 1.4568), in Inconel 718 for high temperature, and with any technical coating the customer requires. Ask our engineering team about lead times for special production runs.
The DIN 6796 standard specifies hardened and tempered C60 carbon steel (or equivalent C67S), with a final hardness range of 420 to 510 HV (Vickers). This hardness level is needed so that the washer can withstand the high stress its function demands without permanent relaxation under prolonged static load.
The modulus of elasticity of stainless steels and Inconel 718 is lower than that of standard C60 steel. This means that, for the same geometry, a 6796 washer in stainless steel or Inconel exerts a somewhat lower residual force than the carbon steel version. This must be taken into account when sizing the joint: if the environment allows C60 + coating, that is usually the optimum solution both technically and economically.
Tell us about your use case and our engineering team will help you choose the optimal solution.
