Dual purpose set detects both mechanical and air induced sounds. Use the black diaphragm chamber and screw-in metal probe to detect mechanical sounds from bearings, engines, transmissions, etc. For air induced sounds, attach the vinyl hose to the hollow tube and funnel assembly. The funnel amplifier will detect noises from vacuum leaks, exhaust leaks, air leaks and wind noise. For hard to reach locations, remove the funnel and use the hollow tube.