Custom Truck One Source Custom Truck One Source (CTOS) is a top manufacturer and distributor of stringing equipment and tools for linemen. Our innovative and highly engineered utility blocks have been sold to electrical utilities and contractors worldwide for over 50 years. In addition, CTOS is a distributor of thousands of linemen tools and accessories made by the industry’s leading manufacturers. CTOS also provides dielectric testing and repair of rubber goods and utility tooling across a nationwide network of six full-service facilities.