Self Guarded One of the more unique style of frogs found on the railroad, the Solid Manganese Self Guarded Frog is typically seen in yards and industries where speed is 30MPH or slower. Cast by the Bethlehem Steel company, this number 10 frog still uses its guide flanges to contact the rims of freight car wheels and safely guide their steel flanges over the frog point at the Opelika transfer yard.