DIN 6885 Parallel Key & Keyway Calculator — Shear and Bearing Strength
DIN 6885 — Drive type feather keys, keyways, deep pattern
Page last updated
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) by shaft diameter, 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.
DIN 6885 is a DIMENSIONAL standard: it contains no strength method, no allowable pressures and no safety factors. The load-capacity calculation for parallel keys is a separate document, DIN 6892, which evaluates surface pressure on the hub groove, the shaft groove and the key flanks. The shear check on the key itself is customary practice from Roloff-Matek (Machine Elements) rather than a clause in either standard. MechanixCalc implements the DIN 6892 hub-pressure check and the Roloff-Matek shear check, with automatic key-section lookup from the DIN 6885 Part 1 table, multi-key load sharing, fit-tolerance correction and a PDF engineering report that states the scope limits.
Calculators that implement DIN 6885
- Shaft Keys CalculatorParallel key shear and hub bearing safety factors by the DIN 6892 method, minimum key length, DIN 6885 auto-dimension lookup, plus Woodruff and spline screening checks (badged as estimates).
- Shaft Analysis CalculatorShaft fatigue check with the Kf stress-concentration factor at the keyway notch — the complementary check alongside the key strength. Uses the modified-Goodman method, not a DIN 743 proof.
What DIN 6885 covers
- Standard key cross-section dimensions (b × h × t1 × t2) by shaft diameter (DIN 6885-1). The MechanixCalc lookup table covers 6–230 mm; outside that range the tool withholds its verdict until you confirm the section
- Tolerance classes for the shaft-keyway and hub-keyway fit: normal, close and loose (DIN 6885-1)
- DIN 6885 contains NO strength rules — load capacity is DIN 6892, and the shear check is Roloff-Matek practice
- Bearing (compressive surface) pressure check — hub keyway flank contact area using the asymmetric DIN geometry (h − t1). MechanixCalc checks the HUB groove only; DIN 6892 also requires the shaft groove and the key flanks
- Shear strength check — tangential load versus key shear area at the shaft–hub interface (Roloff-Matek)
- Multi-key load sharing with the DIN 6892 / Roloff-Matek distribution factor k_s (0.75 for two keys); no third key is credited
- 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 = min(n_keys × k_s, 1.5) = effective number of keys after the load-sharing correction, capped at two keys' worth; τ_allow = min(τ_y / Kt, τ_y) — the key material's shear yield derated by the fit factor and never above that yield; SF_shear = shear safety factor. This shear check is Roloff-Matek practice, not a DIN 6885 or DIN 6892 clause
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), derived in DIN 6892 from the hub yield with a support factor and a load-peak factor; SF_bearing = bearing safety factor. MechanixCalc checks the HUB groove only
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_min is the length at which the safety factor is exactly 1.00, so clearing it is the collapse boundary rather than a pass; L_rec adds a 50 % margin and the 1.5 d rule of thumb — design guidance, in no standard
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. DIN 6885 itself contains no strength rules: the load-capacity calculation is the separate standard DIN 6892 (surface pressure on the hub groove, the shaft groove and the key flanks), and the key-shear check is customary Roloff-Matek practice. Both are 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 bands. A 50 mm shaft falls at the top of the 44–50 mm band and takes a 14 × 9 mm key (b × h) with shaft-keyway depth t1 = 5.5 mm and hub-keyway depth t2 = 3.8 mm; the next band up, over 50 mm to 58 mm, steps to 16 × 10 mm with t1 = 6.0 and t2 = 4.3. The MechanixCalc keys calculator looks the band up automatically from the shaft diameter, so you only need to specify or confirm the key length.
How does multi-key load sharing work for parallel keys?
When two or three keys are fitted at the same section (offset 180° or 120°), manufacturing tolerances prevent equal load distribution. DIN 6892 and Roloff-Matek apply a load-sharing factor k_s — this factor is not in DIN 6885, which carries no strength rules. For two keys k_s = 0.75, giving an effective 1.5 keys; a single key carries its full load (k_s = 1.0). Neither reference credits a third key, because tolerance stack-up means it cannot be shown to carry load, so the calculator caps the credited effective count at two keys' worth. The effective number used in the stress calculation is shown on the tool.
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 included in the free 14-day trial and in every paid plan.
Related standards
Run a DIN 6885 calculation on your own numbers
Free 30-minute preview — no sign-up. A free 14-day account trial unlocks every tool and the branded PDF report.
Open the Shaft KeysUsing MechanixCalc at work? See plans & pricing — one subscription unlocks all 50 calculators, PDF reports and saved projects.