Axles are a great way to tune your kart. Use a softer axle to gain more grip or try a harder axle to free the kart off turns and keep your lap times at their optimum at the end of the race.
As well as being available in a wide option of grades, particular axle grades are available in different lengths. Shorter axles may be better suited to particular tracks or provide an in between grip level that you are chasing. They can also help the kart to feel as though it springs off corners.

AX50XH
AX50M
AX50S
AX50H
AX50XXXS
AX50MS
AX50MH---