That catalog cover refers to "mechanic's" tools, but that word once had a far broader meaning than it tends to now (I worked for a while as a sheet metal worker, and my old-school boss referred to us, and himself, as "mechanics"). Wing dividers were and still should be a common tool in trades less precise than machinist - joiner, tinbender, etc. They have some significant advantages over the machinist's divider when you don't need gnat's-eyebrow precision (although they can, in fact, be set quite precisely).
