The thickness of pomelo trees is related to their fruiting ability. Generally speaking, the thickness of pomelo stem is not the only factor that determines its fruiting ability. The following factors should also be considered:

1. Pomelo tree age: Pomelo trees generally begin to bear fruit at the age of 3-5, and the fruit-bearing ability will gradually increase with the increase of tree age.

2. Supplement nutrition: Pomelo trees need enough nutrition to support fruit growth. Giving pomelo trees enough water, fertilizer and sunshine can improve their fruiting ability.

3. Pruning and fruit thinning: Proper pruning and fruit thinning can help pomelo trees disperse energy and make the fruit grow better. Too much fruit may lead to fruit competition and affect the quality and yield of fruit.

In addition to the above points, it is also necessary to consider the growth environment, climatic conditions and other factors where the grapefruit tree is located. Therefore, the fruit-bearing ability of pomelo can not be determined simply by the thickness of its stem. If you have specific information about the grapefruit tree, you can provide more details, and I can provide you with more accurate answers.