Shell Plates- The thickness can be a problem when working with bottle neck cartridges. To thick & the shoulder can not be pushed back far enough for the round to chamber. To thin & excessive headspace is created, causing case head seperations. A standard shell holder measures .125" +/- .001" So should a shell plate IMO. Dillon Shell Plate. YOU MUST BUY A CARTRIDGE CASE GAGE LIKE AN L. E. WILSON OR A HORNADY COMPARATOR.