a system to accurately align relative to each other a pair of rotary die cylinders having co - acting cutting blades formed by integral lands projecting generally radially outwardly from each cylinder . each cylinder has an alignment groove formed therein such that when the cutting blades of the die cylinders are in alignment , the alignment grooves of each cylinder are aligned and define a slot between the cylinders which is constructed to receive an alignment pin . to initially align the die cylinders relative to each other , they are free to move both axially and rotatably relative to each other to permit the die cylinders to fully engage an alignment pin or pins inserted between the cylinders . preferably , an alignment slot is provided adjacent each end of each cylinder with each slot constructed to receive a separate alignment pin to more accurately register or align the die cylinders relative to each other . with the cylinders fully engaging the alignment pins ensuring accurate alignment of the die cylinders , the bearings and other adjustment and cylinder mounting mechanisms may be locked in position to secure the cylinders in position and the alignment pins subsequently removed prior to operation of the rotary die cylinder machine .