A splined shaft is one that (usually) has equally spaced teeth around the circumference, which are most often parallel to the shaft’s axis of rotation.
Spline Types
Parallel Key Spline: This type has equally spaced teeth that are straight sided. The teeth on the shaft have an equal tooth thickness at any point measured radially out from the axis of rotation.
Involute Spline: Again, this type has equally spaced teeth, but they are not straight sided. The teeth have an involute form, just like a gear tooth.
Crowned Splines: These splines are typically involute. They can be flat root, fillet root, or major diameter fit.
Helical Splines: These can be either parallel or involute tooth form. The helical spline has a specific lead and helix angle.
