Ratchet wheel provided with two ratchets, pawl and half pawl, teaching model / J Schröder, Germany, 1868 Ratchet wheel provided with two ratchets 1868
Model of reversible ratchet wheel provided with Clement's pawl and crank, teaching model / J Schröder, Germany, 1868 Model of reversible ratchet wheel provided with Clement's pawl and crank 1868