an apparatus for processing wafer - shaped articles includes a rotary chuck adapted to hold a wafer shaped article thereon . the rotary chuck includes a peripheral series of pins configured to contact an edge region of a wafer - shaped article . each of the pins projects upwardly from the rotary chuck , and each of the pins is individually secured to the rotary chuck by a respective connecting mechanism . any selected one of the pins can be removed from the rotary chuck by disconnecting its corresponding connecting mechanism without removing any structure of the rotary chuck that surrounds any others of the pins .