The belt is made from industrial strength fiberglass reinforced neoprene, with a pattern of grooves on the inside. The only way it will break is if you intentionally cut it with a knife. It is very strong.
The belt grips tightly to the focus or zoom ring, and there is no chance of slip. The tension can be adjusted to your liking. The belt has grooves in it that match the pattern of grooves on the focus/zoom ring. This provides a non-slip connection.