After one time use, the plastic ring was broken where the metal nut sits, while it was not over-tightened.
This part needs to be able to withstand the strong force of clamping the camera case securely, by a nut and bolt.
The plastic is too hard and brittle. Basically because it's made of second-rate material.
With this defect the device became useless; I had to throw it away unfortunately.
Don't waste your money and spend a bit extra on better quality.