Innovation of the Equal-i-zer Hitch in 1945 and Mobile Manufacturing started by Ed Hedgepeth. First patent filed for in 1951 all rights to Mobile Manufacturing. Mobile Manufacturing changes name to Lindon Hitches in 1984. lindon Hitches changes to Progress Mfg. Inc 2003. These are according to this page. https://www.equalizerhitch.com/images/images/EQ_HistoryOf-Manufacturing_Infographic_170725_182619.jpg
They have been in business for 70+ yrs. So possibly I was mistaken about the hitches as I can't find anything showing what they were a number of years ago although a picture showing the first one shows it with chains but not as we think of them nowadays.