Dakota NDT T-5043-2855 2.25 Mhz, 1/2", Top In, Microdot Non-Magnetic Single Element Contact Transducer. Dakota Ultrasonics single element contact transducers are for use with Mini-Max bolt tension monitors. These transducers are available in magnetic or non-magnetic versions with both versions suitable for fasteners of all metal types. Available sizes include 1/8, 1/4, 3/8, 1/2 and 3/4" diameters. The transducer is also available in 2.25, 5 or 10 MHz versions.