Variable-chamber large round balers typically produce bales from in diameter and up to in width. They did eventually allow milkers, balers, propane gas and pneumatic tires. It also had plants to manufacture hay balers, baby carriages, and brooms. These balers are made of steel with a hydraulic ram to compress the material loaded. These hay balers were in common use up until the late 1980s. At the CLAAS plant in Metz, 400 employees manufacture balers for the agricultural industry. Not all stationary wire tying balers used 2 wires. These balers were marketed for many years by the Ann Arbor Machine Company of Shelbyville. By 1975, fifteen American and Canadian companies were manufacturing large round balers. In the prairies of Canada, the large rectangular balers are also called "prairie raptors". Polysorbate 20 is also used as wetting agent in rubber balers in the elastomer industry. There are different balers used depending on the material type. The first successful pick-up balers were made by the Ann Arbor Company in 1929. Balers are usually pulled by a tractor, with larger balers requiring more powerful tractors. This basic field pick-up mechanism has been used in over 15 million balers.