The Twist-Lock® connector was patented by the Harvey Hubbell company (today, Welcome to Hubbell Wiring Device-Kellems) in 1938. Because it is a locking connector, some prefer it to the stage pin connector. In the 1980s there was a (failed) movement to eliminate the stage pin connector and force all theaters, especially amateur and educational facilities, to convert. Twist-Lock connectors come in a wide varieties of sizes, pin configurations, and voltages, based on a standardized system by NEMA. See this chart, which includes straight blade devices as well (PDF warning): View attachment 2006_NEMA_Chart_Countermat_101107.pdf The most common Twist-Lock connectors used by the entertainment industry are likely the NEMA L5-20 for 120V applications, and L6-20 for moving lights. See also Turn-Lock, for a competing but compatible product.