The horse may also be able to slightly lift the bit in their mouth by stretching the tongue and evading too strong a pressure from rein aids in the short term. Loose rings are suitable for all ...

US Patent US2197248A, 1937. The [Bonham] brothers’ Power Horse tractor. Via Google Patents. But the story of rein-operated tractors was not over, for in the mid-1930s two Utah brothers ...