It gets its Ball Bearing name because it has springs embedded into the rim
with a ball bearing on top of each spring.
The tone ring sits on top of the ball bearings and the head is stretched over that.
The idea was to keep the same tension on the calf-skin head, which was all they had at the time.
Back in the day, banjo players would tighten the head to sound good in one town then, with changing humidity, find it torn when they went to play it in the next town. With this new configuration (24 very strong coil springs, each with a ball bearing on top) when the skin began to react to humidity change, the springs would compress, keeping the head tension the same. This system imparted a unique tone to the banjo. These days it has a plastic head.
James Taylor played this banjo when Neil recorded “Old Man.” Over the years, I was lucky to get to play that part, on my 5-string banjo, whenever Neil played “Old Man” in concerts. One night we were playing at Madison Square Garden. I looked out into the audience and saw James in the 5th row in front of me. No pressure!
These days it is “high strung” meaning the 3rd, 4th and 5th are high octave strings. Most of the time it is tuned down two frets, to D, with the lowest string tuned down 2 more frets, to low C. Neil plays “Old King” on it in the “Heart of Gold” concert movie.