DIN 6885 Parallel Key & Keyway Calculator — Shear and Bearing Strength
DIN 6885 — Drive type feather keys, keyways, deep pattern
DIN 6885 is the German standard for drive-type feather keys (parallel keys) and their keyways — the most widely used form-fit shaft-hub connection in power-transmission machinery. Part 1, published in 1968, defines the standard key cross-sections (width b, height h, shaft-keyway depth t1 and hub-keyway depth t2) for shaft diameters from 6 mm up to 500 mm, the tolerances for normal, close and loose fits, and the material requirements. It is the reference a designer consults first when selecting a key, and the standard most European machinery manufacturers and gear-box builders follow.
The strength evaluation accompanying DIN 6885 — shear of the key and compressive bearing (surface) pressure on the hub keyway flank — is treated in Roloff-Matek (Machine Elements) and in ISO 3912, which is the companion international standard sharing the same key dimensions. MechanixCalc implements the full shear and bearing check, with automatic key-dimension lookup from the DIN 6885 Part 1 table, multi-key load sharing, fit-tolerance correction and a PDF engineering report.
Calculators that implement DIN 6885
- Shaft Keys CalculatorDIN 6885 parallel key shear and bearing safety factors, minimum key length, auto-dimension lookup, Woodruff key (DIN 6888) and spline strength (ISO 4156).
- Shaft Analysis CalculatorDIN 743 shaft fatigue check with Kf stress-concentration factor at the keyway notch — the complementary check alongside the key strength.
What DIN 6885 covers
- Standard key cross-section dimensions (b × h × t1 × t2) for shaft diameters from 6 mm to 500 mm (DIN 6885-1)
- Tolerance classes for the shaft-keyway and hub-keyway fit: normal, close and loose (DIN 6885-1)
- Shear strength check — tangential load versus key shear area at the shaft–hub interface
- Bearing (compressive surface) pressure check — hub keyway flank contact area using the asymmetric DIN geometry (h − t1)
- Multi-key load sharing with the Roloff-Matek distribution factor k_s (0.75 for two keys, 0.67 for three keys)
- Application-factor Ka to amplify the design torque for shock and dynamic loads
Governing formulas
τ = (T_d × 2000) / (d × b × L_eff × n_k_eff) ; SF_shear = τ_allow / τwhere T_d = T × Ka = design torque (N·m); d = shaft diameter (mm); b = key width (mm); L_eff = effective key length (mm); n_k_eff = n_keys × k_s = effective number of keys after load-sharing correction; τ_allow = allowable shear stress of the key material (MPa); SF_shear = shear safety factor
p = (2 × T_d × 1000) / (d × (h − t1) × L_eff × n_k_eff) ; SF_bearing = p_allow / pwhere h = key height (mm); t1 = shaft keyway depth (mm); h − t1 = hub engagement height (the DIN 6885 asymmetric flank height, not the simplified h/2 approximation); p_allow = allowable bearing pressure for the hub material (MPa); SF_bearing = bearing safety factor
L_min = max( L_min_shear , L_min_bearing ) ; L_rec = max(1.5 × L_min , 1.5 × d)where L_min_shear = (2 × T_d × 1000) / (d × b × τ_allow × n_k_eff); L_min_bearing = (2 × T_d × 1000) / (d × (h − t1) × p_allow × n_k_eff); L_rec = recommended design length including a 50 % margin and the 1.5 d rule of thumb
Frequently asked questions
What is DIN 6885 used for?
DIN 6885 specifies the standard cross-section dimensions (b, h, t1, t2) for parallel (feather) keys and their mating shaft and hub keyways for shaft diameters from 6 mm to 500 mm. It is used by mechanical designers to select the correct key size for a shaft-hub torque connection and to define the keyway geometry for machining. The strength evaluation — shear of the key and compressive bearing on the hub flank — is then carried out using the DIN 6885 geometry as input.
What is the difference between shear and bearing failure for a parallel key?
Shear failure occurs when the key slides across the shaft–hub interface plane: it depends on the key width, effective length and the key material's allowable shear stress. Bearing failure is compressive crushing of the hub keyway flank: it depends on the hub engagement height (h − t1 using the asymmetric DIN geometry), effective length and the hub material's allowable bearing pressure. Both modes must be checked — for soft hub materials (cast iron, structural steel) or short key lengths, bearing typically governs.
How does DIN 6885 define the key dimensions for a shaft?
DIN 6885 Part 1 provides a table of standard key cross-sections indexed by shaft diameter ranges. For example, a 50 mm shaft uses a 16 × 10 mm key (b × h) with shaft-keyway depth t1 = 6.0 mm and hub-keyway depth t2 = 4.3 mm. The MechanixCalc keys calculator looks up this table automatically from the shaft diameter so you only need to specify or confirm the key length.
How does multi-key load sharing work under DIN 6885?
When two or three keys are fitted at the same section (offset 180° or 120°), manufacturing tolerances prevent equal load distribution. DIN 6885 and Roloff-Matek apply a load-sharing factor k_s: k_s = 0.75 for two keys (effective 1.5 keys), k_s = 0.67 for three keys (effective 2.0 keys). A single key always carries its full load (k_s = 1.0). The calculator applies this correction automatically and shows the effective number of keys used in the stress calculation.
Is the DIN 6885 shaft keys calculator free?
You can use it during a free 30-minute preview session with no sign-up required, and a free 14-day account trial unlocks every calculator with no credit card needed. The branded PDF engineering report and saved calculations are part of a paid plan.
Related standards
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