Check the technical requirements or tooth parameter annotations on the drawing:
If βₘ = 0° or Spiral angle = 0° is explicitly marked, then it is a Zerol.
If the tooth trace appears curved in the top view (not straight), but the spiral angle is unmarked or labeled as “Zerol type” or “Gleason Zerol”, it can also be identified as a Zerol.
If it is marked as “Straight bevel gear“, then it is not a Zerol.
If no marking is present, identification can be made by measuring the curvature of the tooth trace or by consulting the original design.