Classic Spindle inside a 5 inch float. 5 inch spindle floats are quite rare. This make sense since there were a lot fewer 5 inch floats produced compared to 3 inch and 4 inch floats. It's also less likely for the molten glass to form a filament and stabilize in place (to become a spindle) in larger floats.
This float also has a perfect stamp of WP #11 'Rivermouth' in the common triangular configuration.
Found on Hokkaido Island, Japan.