Keywords: DavidsonPatent1951.jpg Figure 1 of United States Patent 2 543 765 by T O Davidson et al - Winch for convertible draglines and shovels United States Patent Office Issued February 5 1947 United States Patent Office T O Davidson et al inventors Public domain - original work of the US Federal Government All text and figures in US Patents are in the public domain PD-USGov Power shovels |