A rotary chuck for processing wafer-shaped articles comprises a chuck body having a series of gripping pins that are movable by sliding horizontally and in unison relative to the chuck body from a first position in which the gripping pins are relatively more retracted into the chuck body to a second position in which the gripping pins are relatively more extended from the chuck body and in which the gripping pins are positioned so as to support a wafer-shaped article of a predetermined diameter.