Studer OC/S20 The model OC, now known as the S20, was designed as the successor of the model OB. This machine had similar capacities to the OB and still employed a mechanical drive to the table but, like the RHU450 and RHU500, had close coupled drives for the work-head (still accepting W20 collets) and wheel-head. The S20 was also fitted with a pull over internal spindle for rapid deployment. The S20 is a current Studer product.