Determine the status of a phone line by using the Telephone Line Tester. This tester offers an RJ-11 plug for easy insertion into a phone jack. The high-impact ABS housing provides durability. All of Sperry Instruments items are made of durable construction to meet tough job-site conditions. Plastic cable clamps hold harnesses, cables and tubing. Plastic clamps are used in construction, maintenance and assembly-line operations.