🔑 Keys & Keyways DIN 6885

Parallel key dimensions (Form A) per DIN 6885 — surface pressure and shear check

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Shaft & Key

b × h—key cross-section [mm]
t₁ (shaft)—keyway depth [mm]
t₂ (hub)—keyway depth [mm]
d range—shaft diameter [mm]
mm
6 – 500 mm
N·m
mm
Nominal length (Form A)

Results

DIN 6885 Form A — Full table

d range [mm] b [mm] h [mm] t₁ [mm] t₂ [mm] l min [mm] l max [mm]

Background

Surface pressure (otlačení)

The key bears against the keyway walls. With effective length le = l − b (Form A) and supporting depth t (t₁ on the shaft, t₂ on the hub):

p = Mk / (d/2 · le · t · n)

The hub side (smaller depth t₂) usually governs — keep p ≤ pallow for the hub material.

Shear & design notes

  • Key shear: τ = Mk / (d/2 · le · b · n), keep τ ≤ ~70 MPa (steel key).
  • Rule of thumb: key length l ≈ 1.2–1.5 · d.
  • Two keys at 180° share the torque; with real tolerances only ~75% of the second key is reliable — this tool assumes ideal sharing.
  • Form A keys have rounded ends (le = l − b); Form B (square ends) use le = l.