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In fact, although functional and efficient, the [[Crescent Filler]] had its worst flaw in being unpleasant from an aesthetic point of view, and despite a strong promotional campaign that emphasized its merits (Mark Twain, taken as testimonial, endorsed the advantage of it not allowing the pen to roll down from the table) with the appearance of [[lever filler]] pens the sales began to decline increasingly, despite that the new mechanism was inferior from a purely technical point of view.
This is why in 1921 also [[Conklin]] started producing models with a peculiar [[lever filler]] mechanism, ingeniously constructed so that only half of the lever was in the open. With the introduction of the large dimension pens trend started by the [[Duofold]] also [[Conklin]] introduced in 1923 the [[Duragraph]] model. The following year the [[Duragraph]] was renamed as [[Endura]] and the production was converted to celluloid. Initial model were in black or red hard rubber, but soon they were produced in celluloid, with different colors like ''Rosewood'', ''Black & Gold'', ''Lime Green'', ''Lapis blue'' and the rare ''Blue & Gold'' present only on smaller models.
[[Image:Conklin-Endura-Colors-Set.jpg|thumb|A set of [[Endura]]]]