United States patent number 4021092 was assigned to today's PermaLink® plugs and connectors which are classified among the most rugged and safest wiring devices available. They incorporate many of the same features as Ericson® Perma-Tite® 2 and Perma-Grip™ devices and utilize a two screw cable clamp. Perma-Link® plugs and connectors are designed to provide many years of trouble free service in the most demanding industrial and construction environments.