Urim and Thummim

Exodus 28:30 - Also put the Urim and Thummim in the breastpiece, so they may be over Aaron's heart whenever he enters the presence of the LORD. Thus Aaron will always bear the means of making decisions for the Israelites over his heart before the LORD.

This one is almost too obvious to wonder about. Everyone who knows about the Urim and Thummim must wonder about it (actually, about them) because no one knows for certain what Urim and Thummim are.

In Hebrew, the -im suffix makes a noun plural -- much like adding -s in English. So Urim is plural by itself and so is Thummim.

One of the interesting aspects of this is that Moses doesn't explain what Urim and Thummim are. It's as if it's taken for granted that everyone knew. They apparently existed before being included as a feature of the high priest's (Aaron's) garments. They aren't spoken of as if they were something new that God told Moses about on Mt. Sinai. Many other places in the description of the tabernacle and its furnishings God reminded Moses to have them made just as he had been shown on the mountain. Both oral and visual descriptions were given at least partly because these were totally new creations. Not so with the Urim and Thummim. They are mentioned almost matter-of-factly.

I wonder if Urim and Thummim, though widely-known, were perhaps expensive and/or rare. Was there more than one set, but they were all very old, like antiques?

I wonder if they could be used separately; that is, the Urim by themselves or the Thummim by themselves. Did a single Ur(?) ot a single Thum(?) have any use or value? What about just a pair of them -- one Ur together with one Thum?

I wonder if someone would have considered them worth stealing. Did you need special knowledge and/or skill to use them successfully?