This hand-piece fits Haskins-Strand and Food Machinery of America STANDARD DUTY electric fish scalers. These scalers have a round, plastic handle that rotates. It accepts the standard duty core, which is 1/4" at the end. To know which one you have, measure the end of the drive shaft (core). Standard duty is 1/4". HD is 5/16". They are not interchangeable.
To complete, add the Guard for the cutter tool you are using, either the one for the 6 flute tool or more commonly the one for the Diamond or 8 flute tool. See them in Parts.