Why compare categories?

Question

opencart

Good afternoon, there is such a situation. There are products and categories. Some products may have dimensions (For example, bolts, etc.) Therefore, it was decided to display the goods in the card, in the section do not forget to buy goods from the same category. But there are also goods that do not have dimensions, for example, the same drill, and then it was decided to display another block. The question is, there are categories in which goods have sizes and there are categories in which goods do not have sizes. How, by what criteria can they be compared?