ST50
I just went through the exercise. The transducer and control head for the ST50 and ST60 are identical except for the plugs on the connectors. The ST50 has the hardwired plug. The ST60 uses a spade type connector on the back of the control head. You can buy just the transducer, but for a few dollars more buy a new transducer with the ST60 control head. Also, Raymarine is giving a $30.00 rebate on the ST60 equipment.