Increasing thrust with the RG4 drives equipped with the 4-ring option is less expensive than scaling up to a larger size RG3 drive. Nine Uhing RG3 sizes are each available with the 4-ring option. For Uhing models RG315, -20, -22, -30 and -40, there is a slight difference in the length of the drive box when the fourth bearing is added, slightly reducing travel potential if the RG4 drive is selected. For sizes RG350, -60 and -80, the drive boxes for the RG3 and RG4 models have identical dimensions and travel capacities. The extra bearing doubles the thrust by increasing the number of bearing-to-shaft contact points.