VESALA NANOSONDE MPL4-33 (4.6 mm, 33 kHz)NanoSonde MPL4 33 is Vesalas new, worlds tiniest active sonde for small underground ducts. It is only 4. 6 mm in diameter so it is optimal for calibrating 6 mm (inner diameter) fiber optic ducts and to locate their blockages, dents and other problems. MPL4 33 is flexible in the middle so it can navigate tight duct curves down to 170 mm radius. MPL4 33 is intended to be used with the Vesala CL43 Compact Locator and other cable tracers and pipe locators