Schmidt mini 635 D1 ballpoint refill. Fits all pens using the international size D1 (mini) refill. Partial list of pens that use this refill: Cross Multi-Function Pens, Franklin Covey Hinsdale, Kaweco Sport and Liliput, Lamy Multi-Pens, Monteverde Tool Pen, Parker Executive Quattro, Retro 51 Tornado Elite & Touch, Rotring Multi-Pens (Duo, Trio, Quattro), Worther Shorty Ballpoint, and any other pen taking the international-size D1 mini ballpoint refill.
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