Documentation/Modules/Keys & Splines

Keys & Splines

Parallel key and spline torque capacity

Standards catalog

Validation: indicative · Method band: formula

Open calculator

Indicative method: Parallel-key / spline shear and bearing stress capacity screening

Assumptions

  • Linear elastic material behavior unless noted otherwise.
  • User is responsible for load combinations and load factors per the selected design code.
  • Design standard (US/EU/ISO) sets unit defaults and screening check labels — not a full code worksheet.

Limitations

  • Does not replace full DIN 6885 / ANSI B17.1 fit and tolerance worksheets.
  • Professional screening — verify critical shaft-hub connections with code tables.

Engineering checks

CheckINDUSEUISO
Key shear safety factorimplementedimplemented—implemented
Key bearing safety factorimplemented——implemented

Keys & Splines (keys-splines)

Purpose

Calculate torque capacity of parallel keys and splines from shear and bearing stress limits on key, shaft, and hub. Supports rectangular and square keys per ISO 3912 screening.

Physics & theory

Keys transmit torque between shaft and hub through shear in the key and bearing on shaft/hub keyways. Tangential force at shaft diameter . Key shear stress for key width and bearing length .

Bearing stress on shaft or hub side is using key height . Splines multiply effective bearing area by number of teeth with load sharing factor. Stress concentration at keyway corners reduces fatigue strength — static screening only unless Kt applied.

Connections transfer load through bearing, shear, tension, and friction paths depending on joint configuration. Preload in bolted joints reduces joint separation and can allow friction to carry shear; without adequate preload, bolts carry full shear in bearing against hole walls.

FEM-based bolt analysis resolves member and bolt stiffness for load sharing; VDI 2230 provides a systematic worksheet for high-fidelity preloaded joints including embedding loss and tightening scatter.

Governing equations

Numerical method

Closed-form shear and bearing checks for selected key standard size or custom dimensions. Spline mode applies tooth count and load-sharing factor per ISO 3912 simplified method.

Inputs

ParameterDescription
torque, shaft diameterOperating load
Key type/sizeStandard or custom
Material allowablesKey and hub shear/bearing
Spline teeth (optional)For spline analysis

Outputs

  • Tangential force, key shear stress, bearing stress, utilizations, governing failure mode.

Design codes & checks

  • Indicative: Key shear and bearing capacity
  • ISO: ISO 3912 parallel keys and keyways

Assumptions & limitations

  • Uniform load along key length; no torsion along key overhang.
  • Static or slowly varying torque; no fatigue per DIN 6892 full method.
  • Set-screws and taper keys use different models.
  • Hub wall thickness must support bearing — not checked here.

Verification

References

  1. ISO 3912:2019. Parallel keys and keyways.
  2. Shigley, J. E., & Budynas, R. G. Mechanical Engineering Design, 11th ed., Ch. 7.
  3. DIN 6892:2012. Drive type connections — Keys.
  4. Peterson, R. E. Stress Concentration Factors (keyway Kt).
  5. Beer, F. P., et al. Mechanics of Materials, 8th ed. McGraw-Hill — foundational stress and deformation theory.
Maintainer note: Key shear and bearing capacity.