Custom Truck One Source is one of the largest providers of specialty equipment, parts, tools, accessories and services to the electric utility transmission and distribution, telecommunications and rail markets in North America, with a differentiated “one-stop-shop” business model. CTOS offers its specialized equipment to a diverse customer base for the maintenance, repair, upgrade and installation of critical infrastructure assets. Load King is the OEM brand for CTOS, offering a complete line of custom designs. Over 40 CTOS Locations.