G. Boley screw polisher; Germany, first half of the 20th century. Steel and bronze. With wooden case. Measurements: 5 x 20,5 x 7 cm. This tool belongs to the personal collection of Don Juan José Ontalva (Chinchón, 1930- Madrid, 2019), a famous watchmaker from Madrid, descendant of several family generations dedicated to the world of watches. During his career he achieved a high degree of precision and skill, becoming the master of other watchmakers. He is currently recognised for numerous works, including the commissioning and restoration of the Billeter astronomical clock, located in the Congreso de los Diputados (Congress of Deputies).