S13: a ½” (13mm) diameter sonde for narrow ducts and conduits. The S13 Super Small Sonde is designed to be used for tracing the paths of non-metallic pipes, ducts, sewers and drains, and in the precise location of blockages and collapses. The S13 sonde transmits a locate frequency at 33kHz, making it compatible with most Radiodetection Cable and Pipe locators, including the RD8100 Precision Locator range and the C.A.T4 Cable Avoidance Tool range.