The ST600 was originally manufactured exclusively for Raymarine and uses the P120 and B120 housings (2" OD). The insert has two holes in the top along with the pull ring. The cable enters through one of these holes. There are other transducers with this same layout on the top so the Airmar part number on the white cable flag tag should always be consulted to check the transducer identity.
The ST600 has been discontinued and replaced by the ST800. The ST800 inserts are direct replacements for the ST600 inserts within the P120/B120 housings. ST800s have a dome top cap instead of a pull ring.
One key identifier of the ST600 is the existence of two O-rings with different diameters at the top of the insert.