That pin was meant to celebrate May 1st, which is Labour Day or the "Day of National Work" as the Nazis would have put it. The Nazis were violently opposed to organized labour but they courted the support of agrarian and industrial workers nonetheless, and sought to co-opt the latter's yearning for social justice into their totalitarian nationalist ideology — hence the combination of a plough (left) and a hammer with a sword (right). That symbolism was also commonly associated with the völkisch and strasserist fringes of Nazism, though by 1936 it had largely been emptied of its more radical content and become purely official heraldry.