A very devoted and well-researched blog about mechanical pencils (!), Dave’s Mechanical Pencils, brought our attention to this unusual and beautiful example from ca. 1945. Called “The Social Slencil”, the pencil has a flat design (only 2mm thick) to sit in a pocket. It was manufactured by The Slencil Company of Orange, Mass, U.S.A, who still exist.
This seems old for a mechanical pencil but Wikipedia tells us the earliest extant example dates from at least 320 years ago! And the first patent for a refillable pencil with lead-propelling mechanism was issued in Britain in 1822.