[Spangle] Worn? NO
[INJ] Protection? NEARLY NO. One case of this is arguably for protection.

[Charm] NO.

In other words could 2 different people look at the same object and disagree as to whether it was one of these?
I'm trying to think how I can follow your exhortation to focus on one case, I can't actually identify one case well enough to ask about it!

[Raak] Is there writing on it? NO.
[INJ] Could two people disagree? PROBABLY NOT, which is not to say that there aren't alternative words for this.
Well, you could ask me about the metal one, for instance, or the abstract one, or one of the wooden ones.
[Spangle] A label or tag? NO * a sprinkle of applause from a few audients*
[INJ] Container? NO

[Raak] A Load of Symbolics? As above, two cases of this that I can think of have a symbolic function.

Such as a grade of wood, gradings of fruit and vegetables, geades in class and grades of metal?

[FGZstar] A grade? NO.

Please tell me if I'm completely up the wrong tree.

[FGZstar] An inspired guess, but NO (but you're by no means up the wrong tree).

[FGZstar] Holds information? NO. * a pedantic throat clearing from one audience member, who is thinking of one specific case *

[CdM] Disparate Things? YES *applause*, altho they do share a couple more properties than just the name.
[Raak] *checks* YES, you can buy at at least two types of this on Amazon.

[Spangle] YES and NO, depending. You could probably argue it either way for quite a few cases. Unlikely to help!
[Raak] Sometimes plastic? YEEES. I did google an example up of a plastic one, but certainly wouldn't have known that if I hadn't.

[Raak] Hardware? I don't recall seeing one in a hardware store. Then again, I can't say I frequent hardware stores.

[Spangle] I'll pick one of the wooden ones, for which the answer is YES, solid wood.

[Raak] Self-made? NO.

[FGzstar] A wedge? NO, but you are absolutely at the right level of generality.

[Raak] Some day my...? NO, but again, the right level of generality

I'm going to be without net access for a week as of late Thurs evening, so perhaps I can do a summary + hints in case it jogs your thoughts. We are looking for the one-word name for a set of mainly functional objects, (at the same level of generality as "chip" or "wedge"). They can be metal or wood. There are a couple other "vegetable" types which are not wood. All of these are typically smaller than a toaster by volume. There is an abstract type too. You could put The Answer into an Amazon search and be offered a couple of types of this. One of the wooden types of this is all wood and has a musical connection. The metal type has a symbolic function.

... apart from the indefinite article, naturally

[Spangle] Vowelish? NO.