Phelps Style 9620 is a universal lantern ring material that eliminates the need to have lantern rings custom machined.  This product is designed with slits across the width. The slits go against the shaft, act as fluid vents and allow one size to be fit multiple shaft diameters.
To insure a proper fit cut your lantern rings on a mandrel the same diameter as your shaft.  Simply place a ring of the same size as the packing where the flush port vents on the packing set. Universal Lantern Ring Material is as easy to remove as your used packing is with Phelps Style 9640 Flexible Packing Extractors.