Bert Axle 24 -33 - 31.875" 233 - The Bert smart axle has been designed to be used with the Bert smart spool. The 33 spline allows the outside diameter of the axle. It makes it larger with a wall thickness increasing strength and decreasing weight. The axle is equipped with the exclusive Bert shoulder design that allows another length reduction of 2 inches. Switching from the standard 31 spline axle to the revolutionary Bert smart axle means a 5 inch shorter axle which improves weight reduction on the CTD smart tube set up.