Divide into three piles, each pile 15.

Compare the first pile and the second pile, which weight is really in that pile. If the weight is equal, it is really in the third pile.

This can lock the real ring at 15 and then divide it into three piles.

According to the above analysis, it can be locked in 5 boxes after weighing again.

These five are divided into three parts, 1, two parts each, and the third part is 1.

1, 2 copies, whoever weighs is really in the pile. If the weights are equal, the third copy is true.

1, 2 points, two copies of the heavy one are true, just weigh it again.

This is four times heavier at most.