OTHER TYPES OF KEYS
Gib-head keys are square or flat and tapered with a head. The head should not be left exposed so that there is danger that it will catch on workmen’s clothing, possibly resulting in serious injury.

Pin key may either straight or tapered. It is usually a drive fit. Longitudinal assembly at the end of a shaft is easy to do, and in this position, it can transmit heavy power ; size, about one-fourth of the shaft diameter.
Rollpin® one of several patented methods of keying, is driven or pressed into a hole that is small enough to close the slit, assembled in a radial direction.

Saddle keys are tapered, suitable for light power, and are either hollow, with a radius or curvature slightly smaller than the shaft radius or flat, in which case they are assembled on a flat on the shaft.

Kennedy keys are tapered square keys, with or without gib heads. These keys are also said to be tangential keys. Rectangular keys assembled with the diagonal dimension virtually in a circumferential direction are also called tangential keys, and there are other similar ways of assembly.
The Woodruff key, which fits into a semi cylindrical seat in the shaft, is widely used in the automotive and machine tool industries.

A feather key is one that allows the hub to move along the shaft but prevents rotation on the shaft. It is used, for example, to permit moving a gear into or out of engagement with its mate, or to engage and disengage a jaw clutch.

SPLINED SHAFTS
Splines are ridges or teeth[1][2][3] on a drive shaft that mesh with grooves in a mating piece and transfer torque to it, maintaining the angular correspondence between them.
For instance, a gear mounted on a shaft might use a male spline on the shaft that matches the female spline on the gear. The splines on the pictured drive shaft match with the female splines in the center of the clutch plate, while the smooth tip of the axle is supported in the pilot bearing in the flywheel. An alternative to splines is a keyway and key, though splines provide a longer fatigue life.[2]
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Types
There are several types of splines:[2]
Parallel key spline where the sides of the equally-spaced grooves are parallel in both directions, radial and axial.
Involute spline where the sides of the equally-spaced grooves are involute, as with an involute gear, but not as tall. The curves increase strength by decreasing stress concentrations.
Crowned splines where the sides of the equally-spaced grooves are usually involute, but the male teeth are modified to allow for misalignment.
Serrations
where the sides of the equally-spaced grooves form a "V". These are used on small-diameter shafts.
Helical splines where the equally-spaced grooves form a helix about the shaft. The sides may be parallel or involute. This can either minimize stress concentrations for a stationary joint under high load, or allow for rotary and linear motion between the parts.
Ball splines where the 'teeth' of the outer part are implemented with a ball bearing to allow for free linear motion even under high torque.
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[edit]Uses
Drive shafts on vehicles and power take-offs use splines to transmit torque and rotation and allow for changes in length.
Splines are used in several places on bicycles. The crank arm to BB shaft interfaces that are splined include ISIS Drive, Truvativ GXP and Howitzer, Shimano's Octalink and many others, most of which are proprietary. Some cranksets feature modular spiders, where torque is transmitted through splines.Cassettes engage the freehub via a spline that has one groove wider than the others to enforce a fixed orientation. Disc brake mounting interfaces that are splined include Centerlock, by Shimano.
Aircraft engines may have a spline upon which mounts the propeller. There may be a master spline which is wider than the others, so that the propeller may go on at only one orientation, to maintain dynamic balance. This arrangement is commonly found in larger engines, where smaller engines typically use a pattern of threaded fasteners instead.