Label on Outboard Marine Corporation / OMC Gale propeller guard box (their small ring guard).
Houseboat Propeller Regulation Proposed and Withdrawn by USCG: Analysis by PGIC
History of Boat Propeller Safety
Mitigating Boat Propeller Injuries & Fatalities Chart
Approaches to Prevent Outboard Motors From Flipping Into Boats After Striking Floating or Submerged Objects
Why Outboards Used in Bass Tournaments Disproportionately Break Off & Flip into Boats Compared to Other Outboard Motors