STUBAI - The #5509 series are STRAIGHT gouges with a #9 flute or sweep.
Note: The code explained. For a tool designated for example as as a #550912, the 55 is the SERIES, 09 is the SWEEP (curvature) and 12 is the nominal WIDTH in mm at the tip.
Click HERE to go to a Data Sheet on Stubai carving tools. This data sheet will explain the nomenclature used for carving tools of which there are hundreds of variants.
Click HERE to see a .pdf of the makers Series 55 catalogue.