Stewart-Warner was an American manufacturer of vehicle instruments (e.g., gauges and lubricating equipment) and many other products.

The company was founded as Stewart & Clark Company in 1905 by John K. Stewart. Their speedometers were used in the Ford Model T. In 1912 John Stewart joined with Edgar Bassick to make vehicle instruments and horns. Bassick owned Alemite Co. and Stewart had bought the Warner Instrument Company; thus the name was changed to the Stewart-Warner Corporation. The company started in Chicago and built a manufacturing plant on Diversey Parkway. The building kept expanding and finally covered one million square feet (93,000 m²) and six floors. At its peak S-W employed 6000 people at the Diversey complex.[1] They also made radios and refrigerators, among other products, and produced the ubiquitous "zerk" grease fitting, named after its inventor, associated with the company. In the last years of the company's Chicago factory, it owned a number of aging six-spindle Brown & Sharpe and New Britain screw machines.