Thexton 389 Backpressure Test Adapter Kit New test kit aids in diagnosing clogged or restricted exhaust systems Allows comparing backpressure readings ahead and behind of suspected restriction Ideal for diagnosing clogged catalytic converters, collapsed exhaust pipes, etc Kit includes small hole punch for use with air hammer, 5/16" X 1/2" self-tapping bolt and test adapter Use self tapping bolts to plug hole after test is completed