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 has told me that this is there standard. 550 plate dimensions should be .250? thick top to bottom, .132â€ +/- .005â€ from underside of the shellplate to top recess where the die contacts. There info would seem to be wrong from my measurements. Measure your shell plate at each station, each could be different.