Nice 2mm. There are other differences too, alignment of letters with border beads and a shorter trident. There are only 3 basic reverse types (though lots of varieties) for the bronze penny A: Ship & lighthouse - Bun pennies 1860-1894 (34 yrs) B: Just Britannia - old head Vic, Ed VII, George V 1895-1936 (41 yrs) C: Lighthouse - George VI & Eliz 1937-1970 My view is that each series should be treated together for die identification, rather than splitting into reigns