What object was use as a ball in trackball by Tom Cranston Fred Long Staff Kenton Taylor?

The object used as a ball in the trackball invented by Tom Cranston, Fred Longstaff, and Kenton Taylor was a real, solid ball. This is what made it different from the more common "rollerball" mice that came later, which used a set of rollers instead of a free-spinning ball.

This early trackball used a 2.5-inch diameter metal ball that sat on top of a set of sensors. This ball could be rotated in any direction, and the sensors would detect its movement, which was then translated into cursor movement on the screen.

While trackballs with solid balls are not as common today, they were a key development in the early days of computer input devices, paving the way for the rollerball mice and eventually the modern optical and laser mice we use today.