Parallel key · nominal static screening
Parallel-key Nominal Stress Worksheet
Calculate nominal force, key shear and hub-side bearing pressure from documented geometry. DIN 6885-1:2021-11 defines dimensions and tolerances—not a universal allowable stress or automatic design approval.
Derived engineering equations—not DIN formulas
| Quantité | Equation | Units / assumption |
|---|---|---|
| Tangential force | F = T/(d/2) = 2T/d | T in N·mm and d in mm gives F in N. |
| Nominal key shear | τ = F/(bℓeff) | Uniform shear over width × effective loaded length; N/mm² = MPa. |
| Nominal hub-side pressure | p = F/(cℓeff) | Uniform bearing over actual loaded contact height × effective length. |
| Utilisation | u = 100 × demand / entered allowable | Arithmetic comparison only; validity follows the entered design basis. |
| Length from allowable | ℓτ=F/(bτadmissible), ℓp=F/(cpadmissible) | Does not select a standardized total length or key form. |
Dimensional check: N·mm/mm = N; N/(mm·mm) = N/mm² = MPa. Inch-pound inputs are converted internally using NIST factors: 1 ft·lbf = 1.355818 J, 1 in = 25.4 mm and 1 psi = 0.006894757 MPa.
Current DIN family and historical ISO reference
DIN 6885-1:2021-11 is the current corrected 17-page edition for deep-pattern parallel keys, dimensions, tolerances and mass; it replaces DIN 6885-1:2021-06. The family also has DIN 6885-2:2021-06 for deep-pattern machine-tool applications and DIN 6885-3:2021-06 for low pattern. A bare “DIN 6885” label is therefore incomplete. ISO/R 773:1969 was withdrawn on 1998-11-03 and is not a current ISO design authority.
SKF-published DIN 6885/1 reference geometry
The optional helper uses the public SKF Couplings catalog, Table 1. Its intervals are ci-dessus the lower diameter and up to and including the upper diameter. It publishes width b, total key height h and hub keyseat dimension d+t₂. This worksheet uses the listed t₂ as the nominal screening contact height c; the actual drawing and fit must be checked. The catalog is a manufacturer reference, not a substitute for the licensed corrected DIN edition.
| Shaft d, mm (lower exclusive; upper inclusive) | b×h, mm | SKF hub t₂, mm | Shaft d, mm | b×h, mm | t₂, mm |
|---|---|---|---|---|---|
| >6–8 | 2×2 | 1.0 | >95–110 | 28×16 | 6.4 |
| >8–10 | 3×3 | 1.4 | >110–130 | 32×18 | 7.4 |
| >10–12 | 4×4 | 1.8 | >130–150 | 36×20 | 8.4 |
| >12–17 | 5×5 | 2.3 | >150–170 | 40×22 | 9.4 |
| >17–22 | 6×6 | 2.8 | >170–200 | 45×25 | 10.4 |
| >22–30 | 8×7 | 3.3 | >200–230 | 50×28 | 11.4 |
| >30–38 | 10×8 | 3.3 | >230–260 | 56×32 | 12.4 |
| >38–44 | 12×8 | 3.3 | >260–290 | 63×32 | 12.4 |
| >44–50 | 14×9 | 3.8 | >290–330 | 70×36 | 14.4 |
| >50–58 | 16×10 | 4.3 | >330–380 | 80×40 | 15.4 |
| >58–65 | 18×11 | 4.4 | >380–440 | 90×45 | 17.4 |
| >65–75 | 20×12 | 4.9 | >440–550 | 100×50 | 19.5 |
| >75–85 | 22×14 | 5.4 | Outside >6–550 mm: use manual verified geometry. | ||
| >85–95 | 25×14 | 5.4 | Exact forms, lengths, tolerances and acceptance: NEEDS_LICENSED_SOURCE. | ||
Why former rules were removed
The previous calculator used overall length as loaded length, assumed c=h/2, silently clamped every shaft above 200 mm to a 45×25 key, and showed green/red acceptance from arbitrary default allowables. Its inch-pound screen still labelled allowable inputs MPa, so entering psi produced a 145.038× utilization error. Unsupported universal claims for 1–1.5d length, Kt=1.5–2.5 and two keys each carrying 75% were also removed. Effective length, concentration, load sharing and allowable values are design-specific.
