Around 1800 Charles Stanhope, 3rd Earl Stanhope, built the first printing press entirely out of iron. The increased rigidity resulting from the iron, rather than wood construction, further improved the efficiency of the press. Output increased only modestly, from an average of 200 sheets per hour on a wooden hand press to around 250 sheets per hour printing on both sides of the paper on a Stanhope press, with two men working the press. He did not patent his press, and the precise year of its origin is unknown. The earliest surviving example is dated 1804. Early models had straight side frames which were prone to breaking due to the immense pressure that could be exerted. These castings were changed in about 1806 to the heavier rounded style. In this form the press continued to be manufactured into the mid 19th century, and remained in use to a limited extent into the late 19th century.