William Ainsworth, an immigrant from England, began in business as a balance manufacturer in Denver in 1880. The firm became William Ainsworth & Son. in 1905, and continues to this day. Ainsworth began making Brunton pocket transits in the mid-1890s, and they made other surveying instruments during the period 1906-1938.
Ref: Charles Smart, The Makers of Surveying Instruments in America Since 1700 (Troy, 1962), p. 1.