Oxbow stirrups: Narrow stirrups sometimes made of metal and sometimes preferred by bronc riders.
It is designed to promote the release of a caught boot in a drag. Also, the bottom has a five-degree camber, making the desired heels-down position more natural.
Bell stirrups: Wide stirrups common to the buckaroo country. Wide stirrups make it easier to "trot out" for a number of miles in the big country. A long trot is the gait of choice for buckaroos that need to travel long distances horseback to reach the place where they will start to work.
Hope this helps,
Never mind the whales,
SAVE THE COWBOYS