Multiple Items of the Same Kind

https://www.dndbeyond.com/sources/dnd/phb-2024/equipment#MultipleItemsoftheSameKind

:You can’t wear more than one of certain magic items. You can’t normally wear more than one pair of footwear, one pair of gloves or gauntlets, one pair of bracers, one suit of armor, one item of headwear, or one cloak. The DM might make exceptions."

"One item if headwear"???   so 1 crown, 1 helm, or 1 ioun stone? But not all 3.at same time?

How about a robe, a cloak, and a "mantle" of this or that?

Or just 1 of any particular name of.clothing? A mantle is separate from a cloak is separate from a robe?

As always, it’s going to be a DM call. I could maybe see wearing a cloak over a robe as a general thing, for example, but I’d want to look at the specific items to be sure. I couldn’t see wearing a helmet and a crown at the same time, but as the ioun stone is just kind of orbiting, I think it would be fine.

Yeah, this rule is purposefully strict as a baseline, and heavily relies on the DM's call. There are just too many possibilities to address them all, so use common sense.

Ioun Stones for example hover over the player's head. There's no reason to apply any limits to how many you can have (other than the limit of no duplicated attuned items, so no 2 Ioun Stones of Protection). For rings, you can apply the strict RAW ruling (1 ring), the realistic ruling (you have 10 fingers, so 10 rings), or something in between (2 rings max, 1 per hand).

Same thing with the maximum number of helpers you can have when crafting an item, you have this "The DM might make exceptions" mention for emphasis, even though it's true for all the rules in the book.