Shaft connections
Parallel Key Design: Shear Stress vs Bearing Pressure
See how torque creates tangential force in a parallel key and why both key shear and contact pressure should be checked.
Use the calculation tool
Open Parallel Key Calculator →From torque to tangential force
A simplified key calculation first converts shaft torque into tangential force at the shaft radius. That force is then used for the shear and bearing-pressure checks.
Shear check
The simplified shear model distributes tangential force over an effective shear area based on key width and effective length.
Bearing-pressure check
Bearing pressure uses an effective contact height and length. Depending on materials and geometry, the contact-pressure criterion can govern before key shear.
Related standards
DraftFit guides are engineering educational content and do not replace the controlled standard, project specification or responsible-engineer review.