In some missile systems the missile is fired from a telescoping launcher/carrier and must transition from a large tube to a small tube. The aft end of the missile is centered and held in the tube by large detents. The detents are expelled at ignition of the rocket motor and, therefore, a centering system is required for the aft end of the missile until it reaches the entrance ramp of the small tube.
In the past, a sabot type of bore rider was used to guide the missile along the tube. The sabot bore rider also served as a restrainer to hold folding fins in place. However, this device was made of cast foam that was large and cumbersome. Additionally, the device disintegrated when it engaged the shoulder of the smaller tube.