I have made up the sentences below.
(1a) I need some boxes in these sizes for my miscellaneous items.
(1b) I need some boxes of these sizes for my miscellaneous items.
(2a) Crates in these seven specific weights cannot be shipped today.
(2a) Crates of these seven specific weights cannot be shipped today.
Which preposition is correct? Thank you.
Between (1a) and (1b), (1a) is the preferred choice. It's what people generally say when they would like something to be of a certain size. (1b) can work as well and looks like it makes more sense, since a size is a property of an object, but it is not what most people would understand by virtue of its lack of use, in my experience, since they predominately use in. A way to intuitively understand the use of "in" over "of" is to think of a specific size as a category of objects such that those objects have that specific size for its size property. This way, to say "I need some boxes of these sizes for my miscellaneous items" becomes easier to understand if you think about the boxes being objects in the category of objects with "these sizes" as their size for their respective size property. Unfortunately, however, since they are in this category, it would be valid to say that they "of" that category, since they are, in turn, technically properties of that category as objects.
Between (2a) and (2b), (2a) is the preferred choice for the exact reasons above. Simply replace "boxes" with "crates" and "these sizes" with "these seven specific weights."
Now, (1b) and (2b) could work if:
Furthermore, I believe, the second newly constructed sentence, "Crates being of these seven specific weights cannot be shipped today," would benefit from comma punctuation where natural stopping could occur. We would then have: "Crates, being of these seven specific weights, cannot be shipped today."
Hopefully I answered your question satisfactorily.