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Link to Shimano's tech page on the SLX RD-M663: http://si.shimano.com/php/download.php?file=pdf/ev/EV-RD-M663-3043A.pdf
Link to Shimano's tech page on the Deore RD-M593: http://si.shimano.com/php/download.php?file=pdf/ev/EV-RD-M593-3211A.pdf