CDI-511-9766 Spark TesterEnclosed 8 Cyl., adjustable spark gap tester. Has heavy-duty wire for mounting in any position. Helps reduce possibility of igniting gas fumes Adjust from 1/8 in, 1/4 in, 3/8 in and 1/2 in. Requires you to use your existing Spark Plug wiresFeatures: Spark Tester; *For Extension Wires, See 511-9903; Sealed design reduces possibility of fire; Can be used to test 1-8 cylinders; Replaces: 850439; 850439T; 850439T 1; 91-850439;