20 mm Illustration drawn to scale: 40 mm case, 20 mm lugs IWC Ingenieur 1955 movement designer Reference 666 IWC's technical director developed the bidirectional Pellaton automatic winding and the calibre 852 that powered the first Ingenieur under its soft-iron core. 14 or 20 mmStrap size: 14 or 20 mm Source: Christie's, lot essay, IWC Schaffhausen (2015 Ingenieur brochure)