Under DIN EN 16983 (formerly DIN 2093), every conical disc spring is sorted into one of three manufacturing groups by raw stock thickness t, with the cut-offs set at t < 1.25 mm (Group 1), 1.25 mm ≤ t ≤ 6 mm (Group 2), and 6 mm < t ≤ 14 mm (Group 3) [S2][S3]. That single t-band decides production route, allowable material, and whether contact flats are even an option [S2][S7].
For most catalogue buyers the practical meaning is that Group 1 and Group 2 are cold-formed stamped parts, while Group 3 is hot-forged or ring-rolled and almost always ground to final geometry [S2]. Specifying the wrong group for a given bore and load is the most common cause of springs that will not seat flat or that fail in fatigue.
Group Thickness Bands and What They Force on Production
Group 1 covers t < 1.25 mm, Group 2 covers 1.25 mm ≤ t ≤ 6 mm, and Group 3 covers 6 mm < t ≤ 14 mm, with no overlap between the bands [S2][S3]. The standard's own guidance is that "special sizes are also assigned to the appropriate group" if no other production method has been agreed [S2], so a 1.3 mm spring cannot be quietly re-classified as Group 1 even if the engineer would prefer the cold-formed behaviour.
Within Group 1, Springmasters notes that parts are cold formed with radiused edges and supplied without bearing flats [S4], and the carbon-steel restriction in DIN 2093 (C) is explicit: "Carbon steel shall only be used for the manufacture of group 1 springs" [S5]. DIN EN 16983 keeps the same content as DIN 2093:2013-12, since the German standard was incorporated into the European standard "with an unchanged technical content" effective 01.02.2017 [S2].
Contact Flats: Why Only Group 3 Gets Them
Contact flats (also called bearing flats) and the associated reduced disc thickness t1 are a Group 3 feature only. Schnorr's table in DIN EN 16983 spells it out: Group 1 (t < 1.25 mm) no flats, Group 2 (1.25 ≤ t ≤ 6 mm) no flats, Group 3 (6 < t ≤ 14 mm) yes flats [S2]. Disc Springs Mfg's catalogue cross-table reproduces the same rule with the same t-boundaries [S7].
The reason is functional, not aesthetic. On a thick, hot-worked disc the as-formed edges are not flat enough to seat against a parallel mating face; without contact flats the spring will tilt on first load and the calculated flat-flat height l0 will not be reached. On thin cold-formed discs the edges are already flat within tolerance, so the extra machining is unnecessary cost. For more on how flatness at the seat interacts with washer selection, see the entry on spring washers and the broader disc coupling geometry that uses the same conical-spring thinking for torque transmission.
Series A, B, C: The h0/t Ratios Inside Each Group
Within every group the standard recognises three series, defined by the ratio of free cone height h0 to material thickness t: Series A has h0/t ≈ 0.40, Series B has h0/t ≈ 0.75, and Series C has h0/t ≈ 1.30 [S2]. SPIROL restates the same series with a De/t ratio: A is De/t ≈ 18, B is De/t ≈ 28, C is De/t ≈ 40 [S1].
Mechanically, A is the stiffest, flattest disc (lowest deflection per unit load), C is the softest with the most travel, and B sits in the middle. The same nominal outside diameter therefore produces three different load-deflection curves just by changing h0, which is why catalogue pages list the same bore in three rows. Stacks that mix series are common but should be designed, not improvised, because series choice changes the contact pattern under load.
Material and Hardness Windows Set by Group
For steel disc springs, SPIROL's DIN EN 16983 column assigns Group 1 to carbon steel C67S (1.1231 / UNS G10700) with hardness HV 425–510 (HRC 43–50), and Group 2 to alloy steel 51CrV4 (1.8159 / UNS G61500) with hardness HRC 42–52 (HV 412–544) [S1]. Stainless disc springs use SAE 301 full-hard (X10CrNi18-8, 1.4310 / UNS 30100) in both groups and are supplied plain, not oiled [S1].
The DIN 2093 (C) text goes further and ties the elastic-modulus assumption to the material choice: steel springs covered by the standard are "based on a modulus of elasticity E of 206 000 MPa" [S5]. The same clause warns that "the modulus of elasticity and strength property of other materials (e.g. stainless steel for springs in accordance with DIN EN 10151, copper alloys (spring bronze) in accordance with DIN EN 1654) will likely be different" and that the spring manufacturer should be consulted [S5]. For applications such as angular contact bearing preload stacks, that is exactly where the assumption is most often violated.
Decision Matrix: Which Group, and When to Step Up
Use Group 1 when t < 1.25 mm and the bore is small, the load is moderate, and the duty is static or low-cycle: instrument preload, light die springs, and small clamp stacks. Stay with carbon steel C67S at HV 425–510, and do not ask for contact flats because they are not in the standard for this group [S1][S5].
Step up to Group 2 (1.25 mm ≤ t ≤ 6 mm) when the load or the dynamic duty exceeds what a 1 mm-thick carbon-steel disc can carry, or when the design is constrained to a specific De. Switch to 51CrV4 alloy steel at HRC 42–52 to keep fatigue life inside the standard's stress limits, and still without contact flats [S1][S2]. For larger overtravel and softer stacks, choose Series C in this group rather than reducing the disc count.
Move to Group 3 (6 mm < t ≤ 14 mm) when the spring is part of a heavy bolted joint, a large pre-load stack, or any assembly where the seat faces must be flat across a thick cross-section. This is the only group where contact flats and reduced thickness t1 are standard options [S2][S7]. Expect hot forging, ring rolling, and grinding, and accept the cost.
Limits, Failure Modes, and Common Spec Errors
The most common spec error is reading the group from outside diameter instead of from t. Two springs of the same De can sit in different groups purely because of thickness, and the allowable stress, hardness window, and material list all change with the group. A second error is to specify contact flats on a Group 1 or Group 2 spring: the standard does not provide them, so the supplier is being asked to break from DIN EN 16983 geometry [S2][S7].
Dynamic life is governed by the calculated stress at s = 0.75 h0, not at flat-flat, and SPIROL notes that "in the mid range, the usual working range, the actual measured deflection very closely co"incides with the theoretical curve, while outside that band residual stresses pull the two apart [S1]. For fatigue-critical stacks, verify the test point against the load tolerance table in DIN EN 16983, which uses lP = l0 − 0.75·h0 as the test length [S2]. For related tolerances on mating components, the measurement test reference covers the metrology side of those checks.
Sourcing, Standards Status, and Quality Checks
As of 2026, the live standard is DIN EN 16983 (quality requirements, dimensions) paired with DIN EN 16984 (calculation), both of which replaced the old DIN 2093 and DIN 2092 with unchanged technical content on 01.02.2017 [S2]. Catalogue pages still showing "DIN 2093" refer to the same geometry, but new drawings and purchase orders should reference the EN numbers. Cross-reference of Group 1 carbon-steel restriction to EN 10083 / EN 10089 / EN 10132-4 and the E = 206 000 MPa modulus assumption is stated in DIN 2093 (C) [S5].
Buyers should pin three things on every drawing: the group (1, 2, or 3), the series (A, B, or C) with its h0/t target, and the material code from the supplier's DIN EN 16983 table. Without those three, the same part number can resolve to a cold-formed C67S disc in one batch and a hot-forged 51CrV4 disc in the next, and the load-deflection curve will not match. A verifiable next step: request the supplier's lot certificate showing t, h0, l0, and the hardness range, and confirm that the test load F was measured at lP = l0 − 0.75·h0 per [S2].
Background reading: Curved-Jaw Zero-Backlash Coupling vs Straight-Jaw Coupling: Spec Decision Map.