those two varities I found in Forbin als Erler catalogs :
the distance between "den" and frame is 4mm its type a in erler catalog number AJ82A issued 1882.
this one is type b in catalog erler ,also found in forbin catalog issued 1887 the distance between "den" and the frame is 1- 2 mm.
this one I didnt met in both catalogs did any one has information about thw word "den" touch the frame .*** Moved by Staff to a more appropriate forum. ***