Hamilton succeeded three watch firms manufacturing timepieces in the same facilities in Lancaster, PA, including the Lancaster Watch Company. The precursor to the Hamilton Watch Co., the Lancaster, Pennsylvania based Keystone Standard Watch Co., was started by Abram Bitner in 1886 with the purchase of Lancaster Watch Company's factory. Keystone manufactured watches featuring a patented "Dust Proof" design that used a small mica window to cover the only opening in the plate of the movement. Keystone existed until 1891 when the company was sold to Hamilton Watch Company.