These bayonet bulb bases are for original headlights of models 1926-1928. The filaments of these bulbs were — due to technical reasons — not always in the focal point of the reflector. Therefore, the focus of the light beam usually had to be re-adjusted after a bulb exchange. The The Cyclery bulb bases with their spring-loaded adjusting screw take care of this job. The wire cores are clamped with a set screw each.